why no output

Question

def strongBrain ():
    a=input('integer a:\n')
    b=input('integer b:\n')
    c=input('integer c:\n')
    d=input('integer d:\n')
    str=('+','-','*','/')
    flag=1
    for param_1 in str:
        for param_2 in str:
            for param_3 in str:
                formula=a+param_1+b+param_2+c+param_3+d
                value=eval(formula)
                if value==24:
                    flag=0
                    print(formula)
    if flag:
        print('NONE')

Answer 1

The only reason there could be no output is that you defined your function, but forgot to call it:

if __name__ == '__main__':
strongBrain()

Answer 2

Also, let me give you some advice on your code.

1. str is a built in python method and you've reassigned it as your own variable. So, next time you call str() method, it will lead to an error. You should've chosen a different name, for instance, ops or operands.

2. I understand, that you're only starting using python, but still. Your code is too 'c-style'. If you are learning python, try making use of its possibilities and write 'pythonic' style. For instance:

a=input('integer a:\n')
b=input('integer b:\n') #you've typed the same instruction 4 times
c=input('integer c:\n') #which is ugly
d=input('integer d:\n')

a,b,c,d = (input('integer {}:\n'.format(i)) for i in 'abcd') #much prettier

Using flags and too deeply nested loops is also a bad idea. Python allows you to avoid this:

flag=1 #you don't need flags in python

for ...:
for...: #this is too nested
for...:
if...:

So, I have rewritten your code in a python manner and got smth like that:

from itertools import combinations_with_replacement as comb

def pythonic_brain():
a,b,c,d = (input('integer {}:\n'.format(i)) for i in 'abcd')
ops = '+-/*'
f = (a+op1+b+op2+c+op3+d for (op1,op2,op3) in comb(ops,3))
f24 = filter(lambda x: eval(x)==24, f)
if f24:
for i in f24:
print(i)
else:
print('None')

if __name__ == '__main__':
pythonic_brain()

https://code.sololearn.com/c713OqcJ9arV/#py