使用用户输入字符串反向补充 DNA

Question

I want to print the reverse compliment of a user input string of DNA. For Background: Input can be any combination of the characters A C G or T. A and T are compliments and G and C are compliments of one another. My goal is to take the user input and print out the reverse compliment of that string.

So far I have been able to reverse the user input string, but I am unsure of how to apply the compliment. Any help would be greatly appreciated!

print("Enter a DNA string:")

string = str(input("S> "))

reverse_string = (string[::-1])

print(reverse_string)

My code so far prints out the user input string reversed, but not the compliment.

Example input:

S> AAAACCCGGT

My output TGGCCCAAAA

Desired Output ACCGGGTTTT

Answer 1

Just use a dict to map chars to their complements, apply the mapping to the reverse string and str.join the chars back together:

# complement mapping
c = {'A': 'T', 'T': 'A', 'G': 'C', 'C': 'G'}

s = 'AAAACCCGGT'  # do not shadow string module
rev_comp = ''.join(map(c.get, s[::-1]))
# 'ACCGGGTTTT'

Answer 2

The compliment part can be done via a mapping of A -> T (and T -> A) and similarly for G, C. Use a comprehension to build the compliment string and then reverse it.

dna = 'AAAACCCGGT'

compliment_mapping = {'A': 'T', 'T': 'A', 'G': 'C', 'C': 'G'}

compliment = ''.join(compliment_mapping[c] for c in dna)

reverse_compliment = compliment[::-1]

print(reverse_compliment)

Output:

ACCGGGTTTT

Answer 3

You can use a dictionary to store the compliment relationship. In addition, the use of reversed avoids creating a reversed list in the memory, reducing the memory footprint.

print("Enter a DNA string:")
compliment = {'A': 'T', 'T': 'A', 'G': 'C', 'C': 'G'}

while True:
    dna = str(input("S> "))
    reverse_dna = ''.join(compliment[bp] for bp in reversed(dna))
    print(reverse_dna)

Here is the output.

Enter a DNA string:
S> AAAACCCGGT
ACCGGGTTTT
S> ACCGGGTTTT
AAAACCCGGT

You can see that the reverse compliment of the reverse compliment is the original DNA string.