CODEWITHSUNDEEP
pythonfunctionpython-3.xif-statementfor-loop
pixel rain
pixel rain

Reputation: 75

Running a for loop only after an if condition has been met

I'm currently trying to make a very simply testing function that first checks to see if the users input is a multiple of 3, then tests each individual character to see if they are valid characters. Here's my code below:

def is_dna(string):

    string.upper() 
    if(len(string) % 3 == 0):
        print("LENGTH CORRECT")
        for n in string:
            if(n == "A" or n == "T" or n == "C" or n == "G"):
                print("Valid")
            else:
                print("Invalid character")
                break
        return True
    else:
        print("Too many/little characters")
        return False

When run, the bottom section will run fine, and if a correct amount of characters is used this will also successfully print the debug "LENGTH CORRECT" string. The issue is that the for loop will not initialize, and I haven't the foggiest why. Testing just the loop shows it to work fine; what is wrong with this function?

Upvotes: 2

Views: 86

Answers (3)

Rolando Urquiza
Rolando Urquiza

Reputation: 1450

You don't need the cycle, just use regular expressions:

import re

def is_dna(string)
    return re.match("([CAGT]{3})+", string.upper()) is not None

Upvotes: 0

Infinidoge
Infinidoge

Reputation: 56

simple fix you just need to have the string.upper() move into a variable then act upon the variable

code that is fixed

def is_dna(stri):
    string = stri.upper() 
    if(len(string) % 3 == 0):
        print("LENGTH CORRECT")
        for n in string:
            if(n == "A" or n == "T" or n == "C" or n == "G"):
                print("Valid")
            else:
                print("Invalid character")
                break
        return True
    else:
        print("Too many/little characters")
    return False
is_dna("ATCGCTATC") #this works and tests it perfectly

Upvotes: 2

hankym
hankym

Reputation: 149

string = string.upper()

the function upper() just return the uppercase of the character,the string self is not change.

Upvotes: 0

Related Questions