[SOLVED] Pythonic way to replace chars

Pythonic way to replace chars

I want to replace some characters in a string using a pythonic approach.

A -> T
C -> G
G -> C
T -> A

Example:

AAATCGATTGAT

will transform into

TTTAGCTAACTA

What I did:

def swap(string):
    string = re.sub('A', 'aux', string)
    string = re.sub('T', 'A', string)
    string = re.sub('aux', 'T', string)
    string = re.sub('C', 'aux', string)
    string = re.sub('G', 'C', string)
    string = re.sub('aux', 'G', string)

    return string

It worked great, but i'm looking for a more pythonic way to reach that.

Solution

Here's a refactoring of ~~the currently accepted-~~ Chepner's deleted answer which only calls maketrans once.

tt = str.maketrans({"A":"T", "C":"G", "G":"C", "T": "A"})
for s1 in "AGACAT", "TAGGAC", "ACTAGAA":
    print(s1.translate(tt))

Perhaps also point out that you can chain the result from replace, though this is still clumsy and inefficient:

def acgtgca(s1):
    return s1.replace(
        "A", "\ue0fa").replace(
        "G", "\ue0fb").replace(
        "C", "G").replace(
        "T", "A").replace(
        "\ue0fb", "C").replace(
        "\ue0fa", "T")

This avoids using "aux" as a special marker in favor of two arbitrary characters out of the Unicode Private Use Area.

But again, the maketrans method is both neater and more efficient.