python all（）遍历字符串

Question

I would like to iterate through a string and make sure that the string only consists of these letters: 'A','C','G','T'

>>>string = 'm'
>>>nucleotide = ('A','C','G','T')
>>>print(all(nucleotide for i in string))

This is what I entered, but it comes out to be true in the output. Why is that?

Answer 1

You are testing if nucleotide is not empty; you never test i against it.

You'd have to use in to actually see if i is in the tuple:

all(i in nucleotide for i in string)

It'd be more efficient to make nucleotide a set:

nucleotide = {'A', 'C', 'G', 'T'}

More efficient still is to use a regular expression, at which point the whole test is done in C code:

import re

dna_bases = re.compile(r'^[ACGT]+$')

print(dna_bases.fullmatch(string) is not None)  # Python 3.4, use .match for earlier versions.