Chapter 12 Functions in Python

A function is a block of code which only run when it is called. Data can be passed as parameters into a function.

A function can return data as a result.

12.1 Create a function to determine the GC-content of DNA sequence

def cg_content(dna):
    cg_number = dna.count('C') + dna.count('G')
    length = len(dna)
    return float(cg_number/length)
DNA_seq = "CGCTAGTCAGT"
cg_content_val = cg_content(DNA_seq)
print("CG content is: " + str(cg_content_val))

## CG content is: 0.5454545454545454

DNA_seq2 = "CGCTAGTCAGTAAAAAAAAAAAAAAAAAAAAAAAAAATTT"
cg_content_val = cg_content(DNA_seq2)
print("CG content is: " + str(cg_content_val))

## CG content is: 0.15

12.2 Reverse complement

def reverse_complement(seq):
    complement = {"A": "T", "T":"A" ,"C":"G","G":"C"}
    rc_seq = ""
    for base in seq:
        rc_seq = rc_seq+complement[base]
    return rc_seq

DNA_seq = "ACGT"
print("After reverse complement, the sequence is: " + reverse_complement(DNA_seq))

## After reverse complement, the sequence is: TGCA