Reverse complement of DNA strand using Python

In general, a generator expression is simpler than the original code and avoids creating extra list objects. If there can be multiple-character insertions go with the other answers.

complement = {'A': 'T', 'C': 'G', 'G': 'C', 'T': 'A'}
seq = "TCGGGCCC"
reverse_complement = "".join(complement.get(base, base) for base in reversed(seq))

import string
old_chars = "ACGT"
replace_chars = "TGCA"
tab = string.maketrans(old_chars,replace_chars)
print "AAAACCCGGT".translate(tab)[::-1]

that will give you the reverse compliment = ACCGGGTTTT

The other answers are perfectly fine, but if you plan to deal with real DNA sequences I suggest using Biopython. What if you encounter a character like "-", "*" or indefinitions? What if you want to do further manipulations of your sequences? Do you want to create a parser for each file format out there?

The code you ask for is as easy as:

from Bio.Seq import Seq

seq = Seq("TCGGGCCC")

print seq.reverse_complement()
# GGGCCCGA

Now if you want to do another transformations:

print seq.complement()
print seq.transcribe()
print seq.translate()

Outputs

AGCCCGGG
UCGGGCCC
SG

And if you run into strange chars, no need to keep adding code to your program. Biopython deals with it:

seq = Seq("TCGGGCCCX")
print seq.reverse_complement()
# XGGGCCCGA