Bio.Seq module¶

Provide objects to represent biological sequences with alphabets.

See also the Seq wiki and the chapter in our tutorial:

class Bio.Seq.Seq(data, alphabet=Alphabet())¶

Bases: object

Read-only sequence object (essentially a string with an alphabet).

Like normal python strings, our basic sequence object is immutable. This prevents you from doing my_seq[5] = “A” for example, but does allow Seq objects to be used as dictionary keys.

The Seq object provides a number of string like methods (such as count, find, split and strip), which are alphabet aware where appropriate.

In addition to the string like sequence, the Seq object has an alphabet property. This is an instance of an Alphabet class from Bio.Alphabet, for example generic DNA, or IUPAC DNA. This describes the type of molecule (e.g. RNA, DNA, protein) and may also indicate the expected symbols (letters).

The Seq object also provides some biological methods, such as complement, reverse_complement, transcribe, back_transcribe and translate (which are not applicable to sequences with a protein alphabet).

__init__(self, data, alphabet=Alphabet())¶

Create a Seq object.

Arguments:

seq - Sequence, required (string)
alphabet - Optional argument, an Alphabet object from Bio.Alphabet

You will typically use Bio.SeqIO to read in sequences from files as SeqRecord objects, whose sequence will be exposed as a Seq object via the seq property.

However, will often want to create your own Seq objects directly:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> my_seq = Seq("MKQHKAMIVALIVICITAVVAALVTRKDLCEVHIRTGQTEVAVF",
...              IUPAC.protein)
>>> my_seq
Seq('MKQHKAMIVALIVICITAVVAALVTRKDLCEVHIRTGQTEVAVF', IUPACProtein())
>>> print(my_seq)
MKQHKAMIVALIVICITAVVAALVTRKDLCEVHIRTGQTEVAVF
>>> my_seq.alphabet
IUPACProtein()

__repr__(self)¶: Return (truncated) representation of the sequence for debugging.

__str__(self)¶

Return the full sequence as a python string, use str(my_seq).

Note that Biopython 1.44 and earlier would give a truncated version of repr(my_seq) for str(my_seq). If you are writing code which need to be backwards compatible with really old Biopython, you should continue to use my_seq.tostring() as follows:

try:
    # The old way, removed in Biopython 1.73
    as_string = seq_obj.tostring()
except AttributeError:
    # The new way, needs Biopython 1.45 or later.
    # Don't use this on Biopython 1.44 or older as truncates
    as_string = str(seq_obj)

__hash__(self)¶

Hash for comparison.

See the __cmp__ documentation - this has changed from past versions of Biopython!

__eq__(self, other)¶

Compare the sequence to another sequence or a string (README).

Historically comparing Seq objects has done Python object comparison. After considerable discussion (keeping in mind constraints of the Python language, hashes and dictionary support), Biopython now uses simple string comparison (with a warning about the change).

Note that incompatible alphabets (e.g. DNA to RNA) will trigger a warning.

During this transition period, please just do explicit comparisons:

>>> from Bio.Seq import Seq
>>> seq1 = Seq("ACGT")
>>> seq2 = Seq("ACGT")
>>> id(seq1) == id(seq2)
False
>>> str(seq1) == str(seq2)
True

The new behaviour is to use string-like equality:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> seq1 == seq2
True
>>> seq1 == "ACGT"
True
>>> seq1 == Seq("ACGT", generic_dna)
True

__ne__(self, other)¶: Implement the not-equal operand.

__lt__(self, other)¶: Implement the less-than operand.

__le__(self, other)¶: Implement the less-than or equal operand.

__gt__(self, other)¶: Implement the greater-than operand.

__ge__(self, other)¶: Implement the greater-than or equal operand.

__len__(self)¶: Return the length of the sequence, use len(my_seq).

__getitem__(self, index)¶

Return a subsequence of single letter, use my_seq[index].

>>> my_seq = Seq('ACTCGACGTCG')
>>> my_seq[5]
'A'

__add__(self, other)¶

Add another sequence or string to this sequence.

If adding a string to a Seq, the alphabet is preserved:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_protein
>>> Seq("MELKI", generic_protein) + "LV"
Seq('MELKILV', ProteinAlphabet())

When adding two Seq (like) objects, the alphabets are important. Consider this example:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet.IUPAC import unambiguous_dna, ambiguous_dna
>>> unamb_dna_seq = Seq("ACGT", unambiguous_dna)
>>> ambig_dna_seq = Seq("ACRGT", ambiguous_dna)
>>> unamb_dna_seq
Seq('ACGT', IUPACUnambiguousDNA())
>>> ambig_dna_seq
Seq('ACRGT', IUPACAmbiguousDNA())

If we add the ambiguous and unambiguous IUPAC DNA alphabets, we get the more general ambiguous IUPAC DNA alphabet:

>>> unamb_dna_seq + ambig_dna_seq
Seq('ACGTACRGT', IUPACAmbiguousDNA())

However, if the default generic alphabet is included, the result is a generic alphabet:

>>> Seq("") + ambig_dna_seq
Seq('ACRGT')

You can’t add RNA and DNA sequences:

>>> from Bio.Alphabet import generic_dna, generic_rna
>>> Seq("ACGT", generic_dna) + Seq("ACGU", generic_rna)
Traceback (most recent call last):
   ...
TypeError: Incompatible alphabets DNAAlphabet() and RNAAlphabet()

You can’t add nucleotide and protein sequences:

>>> from Bio.Alphabet import generic_dna, generic_protein
>>> Seq("ACGT", generic_dna) + Seq("MELKI", generic_protein)
Traceback (most recent call last):
   ...
TypeError: Incompatible alphabets DNAAlphabet() and ProteinAlphabet()

__radd__(self, other)¶

Add a sequence on the left.

If adding a string to a Seq, the alphabet is preserved:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_protein
>>> "LV" + Seq("MELKI", generic_protein)
Seq('LVMELKI', ProteinAlphabet())

Adding two Seq (like) objects is handled via the __add__ method.

__mul__(self, other)¶

Multiply Seq by integer.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> Seq('ATG') * 2
Seq('ATGATG')
>>> Seq('ATG', generic_dna) * 2
Seq('ATGATG', DNAAlphabet())

__rmul__(self, other)¶

Multiply integer by Seq.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> 2 * Seq('ATG')
Seq('ATGATG')
>>> 2 * Seq('ATG', generic_dna)
Seq('ATGATG', DNAAlphabet())

__imul__(self, other)¶

Multiply Seq in-place.

Note although Seq is immutable, the in-place method is included to match the behaviour for regular Python strings.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> seq = Seq('ATG', generic_dna)
>>> seq *= 2
>>> seq
Seq('ATGATG', DNAAlphabet())

tomutable(self)¶

Return the full sequence as a MutableSeq object.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> my_seq = Seq("MKQHKAMIVALIVICITAVVAAL",
...              IUPAC.protein)
>>> my_seq
Seq('MKQHKAMIVALIVICITAVVAAL', IUPACProtein())
>>> my_seq.tomutable()
MutableSeq('MKQHKAMIVALIVICITAVVAAL', IUPACProtein())

Note that the alphabet is preserved.

count(self, sub, start=0, end=9223372036854775807)¶

Return a non-overlapping count, like that of a python string.

This behaves like the python string method of the same name, which does a non-overlapping count!

For an overlapping search use the newer count_overlap() method.

Returns an integer, the number of occurrences of substring argument sub in the (sub)sequence given by [start:end]. Optional arguments start and end are interpreted as in slice notation.

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

e.g.

>>> from Bio.Seq import Seq
>>> my_seq = Seq("AAAATGA")
>>> print(my_seq.count("A"))
5
>>> print(my_seq.count("ATG"))
1
>>> print(my_seq.count(Seq("AT")))
1
>>> print(my_seq.count("AT", 2, -1))
1

HOWEVER, please note because python strings and Seq objects (and MutableSeq objects) do a non-overlapping search, this may not give the answer you expect:

>>> "AAAA".count("AA")
2
>>> print(Seq("AAAA").count("AA"))
2

An overlapping search, as implemented in .count_overlap(), would give the answer as three!

count_overlap(self, sub, start=0, end=9223372036854775807)¶

Return an overlapping count.

For a non-overlapping search use the count() method.

Returns an integer, the number of occurrences of substring argument sub in the (sub)sequence given by [start:end]. Optional arguments start and end are interpreted as in slice notation.

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

e.g.

>>> from Bio.Seq import Seq
>>> print(Seq("AAAA").count_overlap("AA"))
3
>>> print(Seq("ATATATATA").count_overlap("ATA"))
4
>>> print(Seq("ATATATATA").count_overlap("ATA", 3, -1))
1

Where substrings do not overlap, should behave the same as the count() method:

>>> from Bio.Seq import Seq
>>> my_seq = Seq("AAAATGA")
>>> print(my_seq.count_overlap("A"))
5
>>> my_seq.count_overlap("A") == my_seq.count("A")
True
>>> print(my_seq.count_overlap("ATG"))
1
>>> my_seq.count_overlap("ATG") == my_seq.count("ATG")
True
>>> print(my_seq.count_overlap(Seq("AT")))
1
>>> my_seq.count_overlap(Seq("AT")) == my_seq.count(Seq("AT"))
True
>>> print(my_seq.count_overlap("AT", 2, -1))
1
>>> my_seq.count_overlap("AT", 2, -1) == my_seq.count("AT", 2, -1)
True

HOWEVER, do not use this method for such cases because the count() method is much for efficient.

__contains__(self, char)¶

Implement the ‘in’ keyword, like a python string.

e.g.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna, generic_rna, generic_protein
>>> my_dna = Seq("ATATGAAATTTGAAAA", generic_dna)
>>> "AAA" in my_dna
True
>>> Seq("AAA") in my_dna
True
>>> Seq("AAA", generic_dna) in my_dna
True

Like other Seq methods, this will raise a type error if another Seq (or Seq like) object with an incompatible alphabet is used:

>>> Seq("AAA", generic_rna) in my_dna
Traceback (most recent call last):
   ...
TypeError: Incompatible alphabets DNAAlphabet() and RNAAlphabet()
>>> Seq("AAA", generic_protein) in my_dna
Traceback (most recent call last):
   ...
TypeError: Incompatible alphabets DNAAlphabet() and ProteinAlphabet()

find(self, sub, start=0, end=9223372036854775807)¶

Find method, like that of a python string.

This behaves like the python string method of the same name.

Returns an integer, the index of the first occurrence of substring argument sub in the (sub)sequence given by [start:end].

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

Returns -1 if the subsequence is NOT found.

e.g. Locating the first typical start codon, AUG, in an RNA sequence:

>>> from Bio.Seq import Seq
>>> my_rna = Seq("GUCAUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAGUUG")
>>> my_rna.find("AUG")
3

rfind(self, sub, start=0, end=9223372036854775807)¶

Find from right method, like that of a python string.

This behaves like the python string method of the same name.

Returns an integer, the index of the last (right most) occurrence of substring argument sub in the (sub)sequence given by [start:end].

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

Returns -1 if the subsequence is NOT found.

e.g. Locating the last typical start codon, AUG, in an RNA sequence:

>>> from Bio.Seq import Seq
>>> my_rna = Seq("GUCAUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAGUUG")
>>> my_rna.rfind("AUG")
15

startswith(self, prefix, start=0, end=9223372036854775807)¶

Return True if the Seq starts with the given prefix, False otherwise.

This behaves like the python string method of the same name.

Return True if the sequence starts with the specified prefix (a string or another Seq object), False otherwise. With optional start, test sequence beginning at that position. With optional end, stop comparing sequence at that position. prefix can also be a tuple of strings to try. e.g.

>>> from Bio.Seq import Seq
>>> my_rna = Seq("GUCAUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAGUUG")
>>> my_rna.startswith("GUC")
True
>>> my_rna.startswith("AUG")
False
>>> my_rna.startswith("AUG", 3)
True
>>> my_rna.startswith(("UCC", "UCA", "UCG"), 1)
True

endswith(self, suffix, start=0, end=9223372036854775807)¶

Return True if the Seq ends with the given suffix, False otherwise.

This behaves like the python string method of the same name.

Return True if the sequence ends with the specified suffix (a string or another Seq object), False otherwise. With optional start, test sequence beginning at that position. With optional end, stop comparing sequence at that position. suffix can also be a tuple of strings to try. e.g.

>>> from Bio.Seq import Seq
>>> my_rna = Seq("GUCAUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAGUUG")
>>> my_rna.endswith("UUG")
True
>>> my_rna.endswith("AUG")
False
>>> my_rna.endswith("AUG", 0, 18)
True
>>> my_rna.endswith(("UCC", "UCA", "UUG"))
True

split(self, sep=None, maxsplit=- 1)¶

Split method, like that of a python string.

This behaves like the python string method of the same name.

Return a list of the ‘words’ in the string (as Seq objects), using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done. If maxsplit is omitted, all splits are made.

Following the python string method, sep will by default be any white space (tabs, spaces, newlines) but this is unlikely to apply to biological sequences.

e.g.

>>> from Bio.Seq import Seq
>>> my_rna = Seq("GUCAUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAGUUG")
>>> my_aa = my_rna.translate()
>>> my_aa
Seq('VMAIVMGR*KGAR*L', HasStopCodon(ExtendedIUPACProtein(), '*'))
>>> for pep in my_aa.split("*"):
...     pep
Seq('VMAIVMGR', HasStopCodon(ExtendedIUPACProtein(), '*'))
Seq('KGAR', HasStopCodon(ExtendedIUPACProtein(), '*'))
Seq('L', HasStopCodon(ExtendedIUPACProtein(), '*'))
>>> for pep in my_aa.split("*", 1):
...     pep
Seq('VMAIVMGR', HasStopCodon(ExtendedIUPACProtein(), '*'))
Seq('KGAR*L', HasStopCodon(ExtendedIUPACProtein(), '*'))

See also the upper method.

complement(self)¶

Return the complement sequence by creating a new Seq object.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> my_dna = Seq("CCCCCGATAG", IUPAC.unambiguous_dna)
>>> my_dna
Seq('CCCCCGATAG', IUPACUnambiguousDNA())
>>> my_dna.complement()
Seq('GGGGGCTATC', IUPACUnambiguousDNA())

You can of course used mixed case sequences,

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> my_dna = Seq("CCCCCgatA-GD", generic_dna)
>>> my_dna
Seq('CCCCCgatA-GD', DNAAlphabet())
>>> my_dna.complement()
Seq('GGGGGctaT-CH', DNAAlphabet())

Note in the above example, ambiguous character D denotes G, A or T so its complement is H (for C, T or A).

Trying to complement a protein sequence raises an exception.

>>> my_protein = Seq("MAIVMGR", IUPAC.protein)
>>> my_protein.complement()
Traceback (most recent call last):
   ...
ValueError: Proteins do not have complements!

reverse_complement(self)¶

Return the reverse complement sequence by creating a new Seq object.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> my_dna = Seq("CCCCCGATAGNR", IUPAC.ambiguous_dna)
>>> my_dna
Seq('CCCCCGATAGNR', IUPACAmbiguousDNA())
>>> my_dna.reverse_complement()
Seq('YNCTATCGGGGG', IUPACAmbiguousDNA())

Note in the above example, since R = G or A, its complement is Y (which denotes C or T).

You can of course used mixed case sequences,

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> my_dna = Seq("CCCCCgatA-G", generic_dna)
>>> my_dna
Seq('CCCCCgatA-G', DNAAlphabet())
>>> my_dna.reverse_complement()
Seq('C-TatcGGGGG', DNAAlphabet())

Trying to complement a protein sequence raises an exception:

>>> my_protein = Seq("MAIVMGR", IUPAC.protein)
>>> my_protein.reverse_complement()
Traceback (most recent call last):
   ...
ValueError: Proteins do not have complements!

transcribe(self)¶

Return the RNA sequence from a DNA sequence by creating a new Seq object.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> coding_dna = Seq("ATGGCCATTGTAATGGGCCGCTGAAAGGGTGCCCGATAG",
...                  IUPAC.unambiguous_dna)
>>> coding_dna
Seq('ATGGCCATTGTAATGGGCCGCTGAAAGGGTGCCCGATAG', IUPACUnambiguousDNA())
>>> coding_dna.transcribe()
Seq('AUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAG', IUPACUnambiguousRNA())

Trying to transcribe a protein or RNA sequence raises an exception:

>>> my_protein = Seq("MAIVMGR", IUPAC.protein)
>>> my_protein.transcribe()
Traceback (most recent call last):
   ...
ValueError: Proteins cannot be transcribed!

back_transcribe(self)¶

Return the DNA sequence from an RNA sequence by creating a new Seq object.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> messenger_rna = Seq("AUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAG",
...                     IUPAC.unambiguous_rna)
>>> messenger_rna
Seq('AUGGCCAUUGUAAUGGGCCGCUGAAAGGGUGCCCGAUAG', IUPACUnambiguousRNA())
>>> messenger_rna.back_transcribe()
Seq('ATGGCCATTGTAATGGGCCGCTGAAAGGGTGCCCGATAG', IUPACUnambiguousDNA())

Trying to back-transcribe a protein or DNA sequence raises an exception:

>>> my_protein = Seq("MAIVMGR", IUPAC.protein)
>>> my_protein.back_transcribe()
Traceback (most recent call last):
   ...
ValueError: Proteins cannot be back transcribed!

translate(self, table='Standard', stop_symbol='*', to_stop=False, cds=False, gap=None)¶

Turn a nucleotide sequence into a protein sequence by creating a new Seq object.

This method will translate DNA or RNA sequences, and those with a nucleotide or generic alphabet. Trying to translate a protein sequence raises an exception.

Arguments:

table - Which codon table to use? This can be either a name (string), an NCBI identifier (integer), or a CodonTable object (useful for non-standard genetic codes). This defaults to the “Standard” table.
stop_symbol - Single character string, what to use for terminators. This defaults to the asterisk, “*”.
to_stop - Boolean, defaults to False meaning do a full translation continuing on past any stop codons (translated as the specified stop_symbol). If True, translation is terminated at the first in frame stop codon (and the stop_symbol is not appended to the returned protein sequence).
cds - Boolean, indicates this is a complete CDS. If True, this checks the sequence starts with a valid alternative start codon (which will be translated as methionine, M), that the sequence length is a multiple of three, and that there is a single in frame stop codon at the end (this will be excluded from the protein sequence, regardless of the to_stop option). If these tests fail, an exception is raised.
gap - Single character string to denote symbol used for gaps. It will try to guess the gap character from the alphabet.

e.g. Using the standard table:

>>> coding_dna = Seq("GTGGCCATTGTAATGGGCCGCTGAAAGGGTGCCCGATAG")
>>> coding_dna.translate()
Seq('VAIVMGR*KGAR*', HasStopCodon(ExtendedIUPACProtein(), '*'))
>>> coding_dna.translate(stop_symbol="@")
Seq('VAIVMGR@KGAR@', HasStopCodon(ExtendedIUPACProtein(), '@'))
>>> coding_dna.translate(to_stop=True)
Seq('VAIVMGR', ExtendedIUPACProtein())

Now using NCBI table 2, where TGA is not a stop codon:

>>> coding_dna.translate(table=2)
Seq('VAIVMGRWKGAR*', HasStopCodon(ExtendedIUPACProtein(), '*'))
>>> coding_dna.translate(table=2, to_stop=True)
Seq('VAIVMGRWKGAR', ExtendedIUPACProtein())

In fact, GTG is an alternative start codon under NCBI table 2, meaning this sequence could be a complete CDS:

>>> coding_dna.translate(table=2, cds=True)
Seq('MAIVMGRWKGAR', ExtendedIUPACProtein())

It isn’t a valid CDS under NCBI table 1, due to both the start codon and also the in frame stop codons:

>>> coding_dna.translate(table=1, cds=True)
Traceback (most recent call last):
    ...
Bio.Data.CodonTable.TranslationError: First codon 'GTG' is not a start codon

If the sequence has no in-frame stop codon, then the to_stop argument has no effect:

>>> coding_dna2 = Seq("TTGGCCATTGTAATGGGCCGC")
>>> coding_dna2.translate()
Seq('LAIVMGR', ExtendedIUPACProtein())
>>> coding_dna2.translate(to_stop=True)
Seq('LAIVMGR', ExtendedIUPACProtein())

When translating gapped sequences, the gap character is inferred from the alphabet:

>>> from Bio.Alphabet import Gapped
>>> coding_dna3 = Seq("GTG---GCCATT", Gapped(IUPAC.unambiguous_dna))
>>> coding_dna3.translate()
Seq('V-AI', Gapped(ExtendedIUPACProtein(), '-'))

It is possible to pass the gap character when the alphabet is missing:

>>> coding_dna4 = Seq("GTG---GCCATT")
>>> coding_dna4.translate(gap='-')
Seq('V-AI', Gapped(ExtendedIUPACProtein(), '-'))

NOTE - Ambiguous codons like “TAN” or “NNN” could be an amino acid or a stop codon. These are translated as “X”. Any invalid codon (e.g. “TA?” or “T-A”) will throw a TranslationError.

NOTE - This does NOT behave like the python string’s translate method. For that use str(my_seq).translate(…) instead.

ungap(self, gap=None)¶

Return a copy of the sequence without the gap character(s).

The gap character can be specified in two ways - either as an explicit argument, or via the sequence’s alphabet. For example:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> my_dna = Seq("-ATA--TGAAAT-TTGAAAA", generic_dna)
>>> my_dna
Seq('-ATA--TGAAAT-TTGAAAA', DNAAlphabet())
>>> my_dna.ungap("-")
Seq('ATATGAAATTTGAAAA', DNAAlphabet())

If the gap character is not given as an argument, it will be taken from the sequence’s alphabet (if defined). Notice that the returned sequence’s alphabet is adjusted since it no longer requires a gapped alphabet:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC, Gapped, HasStopCodon
>>> my_pro = Seq("MVVLE=AD*", HasStopCodon(Gapped(IUPAC.protein, "=")))
>>> my_pro
Seq('MVVLE=AD*', HasStopCodon(Gapped(IUPACProtein(), '='), '*'))
>>> my_pro.ungap()
Seq('MVVLEAD*', HasStopCodon(IUPACProtein(), '*'))

Or, with a simpler gapped DNA example:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC, Gapped
>>> my_seq = Seq("CGGGTAG=AAAAAA", Gapped(IUPAC.unambiguous_dna, "="))
>>> my_seq
Seq('CGGGTAG=AAAAAA', Gapped(IUPACUnambiguousDNA(), '='))
>>> my_seq.ungap()
Seq('CGGGTAGAAAAAA', IUPACUnambiguousDNA())

As long as it is consistent with the alphabet, although it is redundant, you can still supply the gap character as an argument to this method:

>>> my_seq
Seq('CGGGTAG=AAAAAA', Gapped(IUPACUnambiguousDNA(), '='))
>>> my_seq.ungap("=")
Seq('CGGGTAGAAAAAA', IUPACUnambiguousDNA())

However, if the gap character given as the argument disagrees with that declared in the alphabet, an exception is raised:

>>> my_seq
Seq('CGGGTAG=AAAAAA', Gapped(IUPACUnambiguousDNA(), '='))
>>> my_seq.ungap("-")
Traceback (most recent call last):
   ...
ValueError: Gap '-' does not match '=' from alphabet

Finally, if a gap character is not supplied, and the alphabet does not define one, an exception is raised:

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import generic_dna
>>> my_dna = Seq("ATA--TGAAAT-TTGAAAA", generic_dna)
>>> my_dna
Seq('ATA--TGAAAT-TTGAAAA', DNAAlphabet())
>>> my_dna.ungap()
Traceback (most recent call last):
   ...
ValueError: Gap character not given and not defined in alphabet

join(self, other)¶

Return a merge of the sequences in other, spaced by the sequence from self.

Accepts all Seq objects and Strings as objects to be concatenated with the spacer

>>> concatenated = Seq('NNNNN').join([Seq("AAA"), Seq("TTT"), Seq("PPP")])
>>> concatenated
Seq('AAANNNNNTTTNNNNNPPP')

Throws error if other is not an iterable and if objects inside of the iterable are not Seq or String objects

class Bio.Seq.UnknownSeq(length, alphabet=Alphabet(), character=None)¶

Bases: Bio.Seq.Seq

Read-only sequence object of known length but unknown contents.

If you have an unknown sequence, you can represent this with a normal Seq object, for example:

>>> my_seq = Seq("N"*5)
>>> my_seq
Seq('NNNNN')
>>> len(my_seq)
5
>>> print(my_seq)
NNNNN

However, this is rather wasteful of memory (especially for large sequences), which is where this class is most useful:

>>> unk_five = UnknownSeq(5)
>>> unk_five
UnknownSeq(5, character='?')
>>> len(unk_five)
5
>>> print(unk_five)
?????

You can add unknown sequence together, provided their alphabets and characters are compatible, and get another memory saving UnknownSeq:

>>> unk_four = UnknownSeq(4)
>>> unk_four
UnknownSeq(4, character='?')
>>> unk_four + unk_five
UnknownSeq(9, character='?')

If the alphabet or characters don’t match up, the addition gives an ordinary Seq object:

>>> unk_nnnn = UnknownSeq(4, character="N")
>>> unk_nnnn
UnknownSeq(4, character='N')
>>> unk_nnnn + unk_four
Seq('NNNN????')

Combining with a real Seq gives a new Seq object:

>>> known_seq = Seq("ACGT")
>>> unk_four + known_seq
Seq('????ACGT')
>>> known_seq + unk_four
Seq('ACGT????')

__init__(self, length, alphabet=Alphabet(), character=None)¶

Create a new UnknownSeq object.

If character is omitted, it is determined from the alphabet, “N” for nucleotides, “X” for proteins, and “?” otherwise.

__len__(self)¶: Return the stated length of the unknown sequence.

__str__(self)¶: Return the unknown sequence as full string of the given length.

__repr__(self)¶: Return (truncated) representation of the sequence for debugging.

__add__(self, other)¶

Add another sequence or string to this sequence.

Adding two UnknownSeq objects returns another UnknownSeq object provided the character is the same and the alphabets are compatible.

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_protein
>>> UnknownSeq(10, generic_protein) + UnknownSeq(5, generic_protein)
UnknownSeq(15, alphabet=ProteinAlphabet(), character='X')

If the characters differ, an UnknownSeq object cannot be used, so a Seq object is returned:

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_protein
>>> UnknownSeq(10, generic_protein) + UnknownSeq(5, generic_protein,
...                                              character="x")
Seq('XXXXXXXXXXxxxxx', ProteinAlphabet())

If adding a string to an UnknownSeq, a new Seq is returned with the same alphabet:

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_protein
>>> UnknownSeq(5, generic_protein) + "LV"
Seq('XXXXXLV', ProteinAlphabet())

__radd__(self, other)¶: Add a sequence on the left.

__mul__(self, other)¶

Multiply UnknownSeq by integer.

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_dna
>>> UnknownSeq(3) * 2
UnknownSeq(6, character='?')
>>> UnknownSeq(3, generic_dna) * 2
UnknownSeq(6, alphabet=DNAAlphabet(), character='N')

__rmul__(self, other)¶

Multiply integer by UnknownSeq.

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_dna
>>> 2 * UnknownSeq(3)
UnknownSeq(6, character='?')
>>> 2 * UnknownSeq(3, generic_dna)
UnknownSeq(6, alphabet=DNAAlphabet(), character='N')

__imul__(self, other)¶

Multiply UnknownSeq in-place.

Note although UnknownSeq is immutable, the in-place method is included to match the behaviour for regular Python strings.

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_dna
>>> seq = UnknownSeq(3, generic_dna)
>>> seq *= 2
>>> seq
UnknownSeq(6, alphabet=DNAAlphabet(), character='N')

__getitem__(self, index)¶

Get a subsequence from the UnknownSeq object.

>>> unk = UnknownSeq(8, character="N")
>>> print(unk[:])
NNNNNNNN
>>> print(unk[5:3])

>>> print(unk[1:-1])
NNNNNN
>>> print(unk[1:-1:2])
NNN

count(self, sub, start=0, end=9223372036854775807)¶

Return a non-overlapping count, like that of a python string.

This behaves like the python string (and Seq object) method of the same name, which does a non-overlapping count!

For an overlapping search use the newer count_overlap() method.

Returns an integer, the number of occurrences of substring argument sub in the (sub)sequence given by [start:end]. Optional arguments start and end are interpreted as in slice notation.

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

>>> "NNNN".count("N")
4
>>> Seq("NNNN").count("N")
4
>>> UnknownSeq(4, character="N").count("N")
4
>>> UnknownSeq(4, character="N").count("A")
0
>>> UnknownSeq(4, character="N").count("AA")
0

HOWEVER, please note because that python strings and Seq objects (and MutableSeq objects) do a non-overlapping search, this may not give the answer you expect:

>>> UnknownSeq(4, character="N").count("NN")
2
>>> UnknownSeq(4, character="N").count("NNN")
1

count_overlap(self, sub, start=0, end=9223372036854775807)¶

Return an overlapping count.

For a non-overlapping search use the count() method.

Returns an integer, the number of occurrences of substring argument sub in the (sub)sequence given by [start:end]. Optional arguments start and end are interpreted as in slice notation.

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

e.g.

>>> from Bio.Seq import UnknownSeq
>>> UnknownSeq(4, character="N").count_overlap("NN")
3
>>> UnknownSeq(4, character="N").count_overlap("NNN")
2

Where substrings do not overlap, should behave the same as the count() method:

>>> UnknownSeq(4, character="N").count_overlap("N")
4
>>> UnknownSeq(4, character="N").count_overlap("N") == UnknownSeq(4, character="N").count("N")
True
>>> UnknownSeq(4, character="N").count_overlap("A")
0
>>> UnknownSeq(4, character="N").count_overlap("A") == UnknownSeq(4, character="N").count("A")
True
>>> UnknownSeq(4, character="N").count_overlap("AA")
0
>>> UnknownSeq(4, character="N").count_overlap("AA") == UnknownSeq(4, character="N").count("AA")
True

complement(self)¶

Return the complement of an unknown nucleotide equals itself.

>>> my_nuc = UnknownSeq(8)
>>> my_nuc
UnknownSeq(8, character='?')
>>> print(my_nuc)
????????
>>> my_nuc.complement()
UnknownSeq(8, character='?')
>>> print(my_nuc.complement())
????????

reverse_complement(self)¶

Return the reverse complement of an unknown sequence.

The reverse complement of an unknown nucleotide equals itself:

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import generic_dna
>>> example = UnknownSeq(6, generic_dna)
>>> print(example)
NNNNNN
>>> print(example.reverse_complement())
NNNNNN

transcribe(self)¶

Return an unknown RNA sequence from an unknown DNA sequence.

>>> my_dna = UnknownSeq(10, character="N")
>>> my_dna
UnknownSeq(10, character='N')
>>> print(my_dna)
NNNNNNNNNN
>>> my_rna = my_dna.transcribe()
>>> my_rna
UnknownSeq(10, alphabet=RNAAlphabet(), character='N')
>>> print(my_rna)
NNNNNNNNNN

back_transcribe(self)¶

Return an unknown DNA sequence from an unknown RNA sequence.

>>> my_rna = UnknownSeq(20, character="N")
>>> my_rna
UnknownSeq(20, character='N')
>>> print(my_rna)
NNNNNNNNNNNNNNNNNNNN
>>> my_dna = my_rna.back_transcribe()
>>> my_dna
UnknownSeq(20, alphabet=DNAAlphabet(), character='N')
>>> print(my_dna)
NNNNNNNNNNNNNNNNNNNN

upper(self)¶

Return an upper case copy of the sequence.

>>> from Bio.Alphabet import generic_dna
>>> from Bio.Seq import UnknownSeq
>>> my_seq = UnknownSeq(20, generic_dna, character="n")
>>> my_seq
UnknownSeq(20, alphabet=DNAAlphabet(), character='n')
>>> print(my_seq)
nnnnnnnnnnnnnnnnnnnn
>>> my_seq.upper()
UnknownSeq(20, alphabet=DNAAlphabet(), character='N')
>>> print(my_seq.upper())
NNNNNNNNNNNNNNNNNNNN

This will adjust the alphabet if required. See also the lower method.

lower(self)¶

Return a lower case copy of the sequence.

This will adjust the alphabet if required:

>>> from Bio.Alphabet import IUPAC
>>> from Bio.Seq import UnknownSeq
>>> my_seq = UnknownSeq(20, IUPAC.extended_protein)
>>> my_seq
UnknownSeq(20, alphabet=ExtendedIUPACProtein(), character='X')
>>> print(my_seq)
XXXXXXXXXXXXXXXXXXXX
>>> my_seq.lower()
UnknownSeq(20, alphabet=ProteinAlphabet(), character='x')
>>> print(my_seq.lower())
xxxxxxxxxxxxxxxxxxxx

See also the upper method.

translate(self, **kwargs)¶

Translate an unknown nucleotide sequence into an unknown protein.

e.g.

>>> my_seq = UnknownSeq(9, character="N")
>>> print(my_seq)
NNNNNNNNN
>>> my_protein = my_seq.translate()
>>> my_protein
UnknownSeq(3, alphabet=ProteinAlphabet(), character='X')
>>> print(my_protein)
XXX

In comparison, using a normal Seq object:

>>> my_seq = Seq("NNNNNNNNN")
>>> print(my_seq)
NNNNNNNNN
>>> my_protein = my_seq.translate()
>>> my_protein
Seq('XXX', ExtendedIUPACProtein())
>>> print(my_protein)
XXX

ungap(self, gap=None)¶

Return a copy of the sequence without the gap character(s).

The gap character can be specified in two ways - either as an explicit argument, or via the sequence’s alphabet. For example:

>>> from Bio.Seq import UnknownSeq
>>> from Bio.Alphabet import Gapped, generic_dna
>>> my_dna = UnknownSeq(20, Gapped(generic_dna, "-"))
>>> my_dna
UnknownSeq(20, alphabet=Gapped(DNAAlphabet(), '-'), character='N')
>>> my_dna.ungap()
UnknownSeq(20, alphabet=DNAAlphabet(), character='N')
>>> my_dna.ungap("-")
UnknownSeq(20, alphabet=DNAAlphabet(), character='N')

If the UnknownSeq is using the gap character, then an empty Seq is returned:

>>> my_gap = UnknownSeq(20, Gapped(generic_dna, "-"), character="-")
>>> my_gap
UnknownSeq(20, alphabet=Gapped(DNAAlphabet(), '-'), character='-')
>>> my_gap.ungap()
Seq('', DNAAlphabet())
>>> my_gap.ungap("-")
Seq('', DNAAlphabet())

Notice that the returned sequence’s alphabet is adjusted to remove any explicit gap character declaration.

join(self, other)¶

Return a merge of the sequences in other, spaced by the sequence from self.

Accepts Seq/UnknownSeq objects and Strings as objects to be concatenated with the spacer

>>> concatenated = UnknownSeq(5).join([Seq("AAA"), Seq("TTT"), Seq("PPP")])
>>> concatenated
Seq('AAA?????TTT?????PPP')

Throws error if other is not an iterable and if objects inside of the iterable are not Seq/UnknownSeq or String objects.

Will only return an UnknownSeq object of all of the objects to be joined are also UnknownSeqs with the same character as the spacer, similar to how the addition of an UnknownSeq and another UnknownSeq would work.

class Bio.Seq.MutableSeq(data, alphabet=Alphabet())¶

Bases: object

An editable sequence object (with an alphabet).

Unlike normal python strings and our basic sequence object (the Seq class) which are immutable, the MutableSeq lets you edit the sequence in place. However, this means you cannot use a MutableSeq object as a dictionary key.

>>> from Bio.Seq import MutableSeq
>>> from Bio.Alphabet import generic_dna
>>> my_seq = MutableSeq("ACTCGTCGTCG", generic_dna)
>>> my_seq
MutableSeq('ACTCGTCGTCG', DNAAlphabet())
>>> my_seq[5]
'T'
>>> my_seq[5] = "A"
>>> my_seq
MutableSeq('ACTCGACGTCG', DNAAlphabet())
>>> my_seq[5]
'A'
>>> my_seq[5:8] = "NNN"
>>> my_seq
MutableSeq('ACTCGNNNTCG', DNAAlphabet())
>>> len(my_seq)
11

Note that the MutableSeq object does not support as many string-like or biological methods as the Seq object.

__init__(self, data, alphabet=Alphabet())¶: Initialize the class.

__repr__(self)¶: Return (truncated) representation of the sequence for debugging.

__str__(self)¶

Return the full sequence as a python string.

Note that Biopython 1.44 and earlier would give a truncated version of repr(my_seq) for str(my_seq). If you are writing code which needs to be backwards compatible with old Biopython, you should continue to use my_seq.tostring() rather than str(my_seq).

__eq__(self, other)¶

Compare the sequence to another sequence or a string (README).

Currently if compared to another sequence the alphabets must be compatible. Comparing DNA to RNA, or Nucleotide to Protein will raise an exception. Otherwise only the sequence itself is compared, not the precise alphabet.

A future release of Biopython will change this (and the Seq object etc) to use simple string comparison. The plan is that comparing sequences with incompatible alphabets (e.g. DNA to RNA) will trigger a warning but not an exception.

During this transition period, please just do explicit comparisons:

>>> seq1 = MutableSeq("ACGT")
>>> seq2 = MutableSeq("ACGT")
>>> id(seq1) == id(seq2)
False
>>> str(seq1) == str(seq2)
True

Biopython now does:

>>> seq1 == seq2
True
>>> seq1 == Seq("ACGT")
True
>>> seq1 == "ACGT"
True

__ne__(self, other)¶: Implement the not-equal operand.

__lt__(self, other)¶: Implement the less-than operand.

__le__(self, other)¶: Implement the less-than or equal operand.

__gt__(self, other)¶: Implement the greater-than operand.

__ge__(self, other)¶: Implement the greater-than or equal operand.

__len__(self)¶: Return the length of the sequence, use len(my_seq).

__getitem__(self, index)¶

Return a subsequence of single letter, use my_seq[index].

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq[5]
'A'

__setitem__(self, index, value)¶

Set a subsequence of single letter via value parameter.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq[0] = 'T'
>>> my_seq
MutableSeq('TCTCGACGTCG')

__delitem__(self, index)¶

Delete a subsequence of single letter.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> del my_seq[0]
>>> my_seq
MutableSeq('CTCGACGTCG')

__add__(self, other)¶

Add another sequence or string to this sequence.

Returns a new MutableSeq object.

__radd__(self, other)¶

Add a sequence on the left.

>>> from Bio.Seq import MutableSeq
>>> from Bio.Alphabet import generic_protein
>>> "LV" + MutableSeq("MELKI", generic_protein)
MutableSeq('LVMELKI', ProteinAlphabet())

__mul__(self, other)¶

Multiply MutableSeq by integer.

Note this is not in-place and returns a new object, matching native Python list multiplication.

>>> from Bio.Seq import MutableSeq
>>> from Bio.Alphabet import generic_dna
>>> MutableSeq('ATG') * 2
MutableSeq('ATGATG')
>>> MutableSeq('ATG', generic_dna) * 2
MutableSeq('ATGATG', DNAAlphabet())

__rmul__(self, other)¶

Multiply integer by MutableSeq.

Note this is not in-place and returns a new object, matching native Python list multiplication.

>>> from Bio.Seq import MutableSeq
>>> from Bio.Alphabet import generic_dna
>>> 2 * MutableSeq('ATG')
MutableSeq('ATGATG')
>>> 2 * MutableSeq('ATG', generic_dna)
MutableSeq('ATGATG', DNAAlphabet())

__imul__(self, other)¶

Multiply MutableSeq in-place.

>>> from Bio.Seq import MutableSeq
>>> from Bio.Alphabet import generic_dna
>>> seq = MutableSeq('ATG', generic_dna)
>>> seq *= 2
>>> seq
MutableSeq('ATGATG', DNAAlphabet())

append(self, c)¶

Add a subsequence to the mutable sequence object.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq.append('A')
>>> my_seq
MutableSeq('ACTCGACGTCGA')

No return value.

insert(self, i, c)¶

Add a subsequence to the mutable sequence object at a given index.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq.insert(0,'A')
>>> my_seq
MutableSeq('AACTCGACGTCG')
>>> my_seq.insert(8,'G')
>>> my_seq
MutableSeq('AACTCGACGGTCG')

No return value.

pop(self, i=- 1)¶

Remove a subsequence of a single letter at given index.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq.pop()
'G'
>>> my_seq
MutableSeq('ACTCGACGTC')
>>> my_seq.pop()
'C'
>>> my_seq
MutableSeq('ACTCGACGT')

Returns the last character of the sequence

remove(self, item)¶

Remove a subsequence of a single letter from mutable sequence.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq.remove('C')
>>> my_seq
MutableSeq('ATCGACGTCG')
>>> my_seq.remove('A')
>>> my_seq
MutableSeq('TCGACGTCG')

No return value.

count(self, sub, start=0, end=9223372036854775807)¶

Return a non-overlapping count, like that of a python string.

This behaves like the python string method of the same name, which does a non-overlapping count!

For an overlapping search use the newer count_overlap() method.

Returns an integer, the number of occurrences of substring argument sub in the (sub)sequence given by [start:end]. Optional arguments start and end are interpreted as in slice notation.

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

e.g.

>>> from Bio.Seq import MutableSeq
>>> my_mseq = MutableSeq("AAAATGA")
>>> print(my_mseq.count("A"))
5
>>> print(my_mseq.count("ATG"))
1
>>> print(my_mseq.count(Seq("AT")))
1
>>> print(my_mseq.count("AT", 2, -1))
1

HOWEVER, please note because that python strings, Seq objects and MutableSeq objects do a non-overlapping search, this may not give the answer you expect:

>>> "AAAA".count("AA")
2
>>> print(MutableSeq("AAAA").count("AA"))
2

An overlapping search would give the answer as three!

count_overlap(self, sub, start=0, end=9223372036854775807)¶

Return an overlapping count.

For a non-overlapping search use the count() method.

Returns an integer, the number of occurrences of substring argument sub in the (sub)sequence given by [start:end]. Optional arguments start and end are interpreted as in slice notation.

Arguments:

sub - a string or another Seq object to look for
start - optional integer, slice start
end - optional integer, slice end

e.g.

>>> from Bio.Seq import MutableSeq
>>> print(MutableSeq("AAAA").count_overlap("AA"))
3
>>> print(MutableSeq("ATATATATA").count_overlap("ATA"))
4
>>> print(MutableSeq("ATATATATA").count_overlap("ATA", 3, -1))
1

Where substrings do not overlap, should behave the same as the count() method:

>>> from Bio.Seq import MutableSeq
>>> my_mseq = MutableSeq("AAAATGA")
>>> print(my_mseq.count_overlap("A"))
5
>>> my_mseq.count_overlap("A") == my_mseq.count("A")
True
>>> print(my_mseq.count_overlap("ATG"))
1
>>> my_mseq.count_overlap("ATG") == my_mseq.count("ATG")
True
>>> print(my_mseq.count_overlap(Seq("AT")))
1
>>> my_mseq.count_overlap(Seq("AT")) == my_mseq.count(Seq("AT"))
True
>>> print(my_mseq.count_overlap("AT", 2, -1))
1
>>> my_mseq.count_overlap("AT", 2, -1) == my_mseq.count("AT", 2, -1)
True

HOWEVER, do not use this method for such cases because the count() method is much for efficient.

index(self, item)¶

Return first occurrence position of a single entry (i.e. letter).

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq.index('A')
0
>>> my_seq.index('T')
2

Note unlike a Biopython Seq object, or Python string, multi-letter subsequences are not supported.

reverse(self)¶

Modify the mutable sequence to reverse itself.

No return value.

complement(self)¶

Modify the mutable sequence to take on its complement.

Trying to complement a protein sequence raises an exception.

No return value.

reverse_complement(self)¶

Modify the mutable sequence to take on its reverse complement.

Trying to reverse complement a protein sequence raises an exception.

No return value.

extend(self, other)¶

Add a sequence to the original mutable sequence object.

>>> my_seq = MutableSeq('ACTCGACGTCG')
>>> my_seq.extend('A')
>>> my_seq
MutableSeq('ACTCGACGTCGA')
>>> my_seq.extend('TTT')
>>> my_seq
MutableSeq('ACTCGACGTCGATTT')

No return value.

toseq(self)¶

Return the full sequence as a new immutable Seq object.

>>> from Bio.Seq import Seq
>>> from Bio.Alphabet import IUPAC
>>> my_mseq = MutableSeq("MKQHKAMIVALIVICITAVVAAL",
...                      IUPAC.protein)
>>> my_mseq
MutableSeq('MKQHKAMIVALIVICITAVVAAL', IUPACProtein())
>>> my_mseq.toseq()
Seq('MKQHKAMIVALIVICITAVVAAL', IUPACProtein())

Note that the alphabet is preserved.

join(self, other)¶

Return a merge of the sequences in other, spaced by the sequence from self.

Accepts all Seq objects and Strings as objects to be concatenated with the spacer

>>> concatenated = MutableSeq('NNNNN').join([Seq("AAA"), Seq("TTT"), Seq("PPP")])
>>> concatenated
Seq('AAANNNNNTTTNNNNNPPP')

Throws error if other is not an iterable and if objects inside of the iterable are not Seq or String objects

__hash__ = None¶

Bio.Seq.transcribe(dna)¶

Transcribe a DNA sequence into RNA.

If given a string, returns a new string object.

Given a Seq or MutableSeq, returns a new Seq object with an RNA alphabet.

Trying to transcribe a protein or RNA sequence raises an exception.

e.g.

>>> transcribe("ACTGN")
'ACUGN'

Bio.Seq.back_transcribe(rna)¶

Return the RNA sequence back-transcribed into DNA.

If given a string, returns a new string object.

Given a Seq or MutableSeq, returns a new Seq object with an RNA alphabet.

Trying to transcribe a protein or DNA sequence raises an exception.

e.g.

>>> back_transcribe("ACUGN")
'ACTGN'

Bio.Seq.translate(sequence, table='Standard', stop_symbol='*', to_stop=False, cds=False, gap=None)¶

Translate a nucleotide sequence into amino acids.

If given a string, returns a new string object. Given a Seq or MutableSeq, returns a Seq object with a protein alphabet.

Arguments:

table - Which codon table to use? This can be either a name (string), an NCBI identifier (integer), or a CodonTable object (useful for non-standard genetic codes). Defaults to the “Standard” table.
stop_symbol - Single character string, what to use for any terminators, defaults to the asterisk, “*”.
to_stop - Boolean, defaults to False meaning do a full translation continuing on past any stop codons (translated as the specified stop_symbol). If True, translation is terminated at the first in frame stop codon (and the stop_symbol is not appended to the returned protein sequence).
cds - Boolean, indicates this is a complete CDS. If True, this checks the sequence starts with a valid alternative start codon (which will be translated as methionine, M), that the sequence length is a multiple of three, and that there is a single in frame stop codon at the end (this will be excluded from the protein sequence, regardless of the to_stop option). If these tests fail, an exception is raised.
gap - Single character string to denote symbol used for gaps. Defaults to None.

A simple string example using the default (standard) genetic code:

>>> coding_dna = "GTGGCCATTGTAATGGGCCGCTGAAAGGGTGCCCGATAG"
>>> translate(coding_dna)
'VAIVMGR*KGAR*'
>>> translate(coding_dna, stop_symbol="@")
'VAIVMGR@KGAR@'
>>> translate(coding_dna, to_stop=True)
'VAIVMGR'

Now using NCBI table 2, where TGA is not a stop codon:

>>> translate(coding_dna, table=2)
'VAIVMGRWKGAR*'
>>> translate(coding_dna, table=2, to_stop=True)
'VAIVMGRWKGAR'

In fact this example uses an alternative start codon valid under NCBI table 2, GTG, which means this example is a complete valid CDS which when translated should really start with methionine (not valine):

>>> translate(coding_dna, table=2, cds=True)
'MAIVMGRWKGAR'

Note that if the sequence has no in-frame stop codon, then the to_stop argument has no effect:

>>> coding_dna2 = "GTGGCCATTGTAATGGGCCGC"
>>> translate(coding_dna2)
'VAIVMGR'
>>> translate(coding_dna2, to_stop=True)
'VAIVMGR'

NOTE - Ambiguous codons like “TAN” or “NNN” could be an amino acid or a stop codon. These are translated as “X”. Any invalid codon (e.g. “TA?” or “T-A”) will throw a TranslationError.

It will however translate either DNA or RNA.

NOTE - Since version 1.71 Biopython contains codon tables with ‘ambiguous stop codons’. These are stop codons with unambiguous sequence but which have a context dependent coding as STOP or as amino acid. With these tables ‘to_stop’ must be False (otherwise a ValueError is raised). The dual coding codons will always be translated as amino acid, except for ‘cds=True’, where the last codon will be translated as STOP.

>>> coding_dna3 = "ATGGCACGGAAGTGA"
>>> translate(coding_dna3)
'MARK*'

>>> translate(coding_dna3, table=27)  # Table 27: TGA -> STOP or W
'MARKW'

It will however raise a BiopythonWarning (not shown).

>>> translate(coding_dna3, table=27, cds=True)
'MARK'

>>> translate(coding_dna3, table=27, to_stop=True)
Traceback (most recent call last):
   ...
ValueError: You cannot use 'to_stop=True' with this table ...

Bio.Seq.reverse_complement(sequence)¶

Return the reverse complement sequence of a nucleotide string.

If given a string, returns a new string object. Given a Seq or a MutableSeq, returns a new Seq object with the same alphabet.

Supports unambiguous and ambiguous nucleotide sequences.

e.g.

>>> reverse_complement("ACTG-NH")
'DN-CAGT'

Bio.Seq.complement(sequence)¶

Return the complement sequence of a nucleotide string.

If given a string, returns a new string object. Given a Seq or a MutableSeq, returns a new Seq object with the same alphabet.

Supports unambiguous and ambiguous nucleotide sequences.

e.g.

>>> complement("ACTG-NH")
'TGAC-ND'