how to call function b def a(): x = "hello" def b(): return "by"

Here is how to call function 'b' inside function 'a':

def a():
    x = "hello"
    
    def b():
        return "by"
    
    # Call function 'b' inside function 'a'
    result = b()
    return result

# Call function 'a'
output = a()
print(output)  # Output: "by"

In this code, we call function 'b' inside function 'a' and store its return value in the variable result. Then, we return the value of result from function 'a'. Finally, we call function 'a' and print its output.