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Python Conditional Check

Posted by Nick Evershed
Nick Evershed
6,429 Points

print_hello() not defined

Why is it not defined when we just imported it at the beginning?

def print_hello(): print("Hello from app.")
print_hello() if name == 'main':

import app

print("Hello from the second_app") print_hello()

3 Answers

Jamie Grant
Jamie Grant
1,605 Points
Jamie Grant
Jamie Grant
1,605 Points

You're if statement logic is around the wrong way.

You've written -

print_hello() if name == 'main':

It should be

if name == 'main': print_hello()

amyyxt
amyyxt
2,227 Points

Nick Evershed was trying to use the ternary operator for the if line, which is fine. However, there was a syntax error with that as no colons are needed and an "else ..." is required. For example, he can correct this syntax error by writing: print_hello() if name == "main" else print("") Note that what follows "else" cannot be keywords like "pass," "break," or "continue."

givens
givens
7,484 Points
givens
givens
7,484 Points

Order matters. There's also a syntax error with

__name__ == "__main__".

Try copying it down exactly as he wrote it -- in two separate files. You can do this by pausing the video when the code is shown.

In app.py, print(__name__) is __main__. In second_app.py, print(__name__) is app.

I would guess the name is app because it is importing a file with filename "app" dot py. Because __name__ has two different results depending on import or not, you can check this. 

if __name__ == "__main__":
    do_blah()

__name__ is only __main__ in app.py. Therefore, this code will only run if you are in app.py but not imports. This is useful because we want imports to behave differently in many cases.

amyyxt
amyyxt
2,227 Points
amyyxt
amyyxt
2,227 Points

Note that the function print_hello() is defined in app.py, not second_app.py. So, when calling it from second_app.py, you need to tell the machine that you want the print_hello() function from app.py by writing "app.print_hello()" rather than simply "print_hello()." (And, of course, the function must have been imported, which you have done.)