Can't figure out an "if/else" statement

Question

PYTHON: Trying to calculate the period it takes for a pendulum to swing on different planets, I'm extremely new at this so there may be an easy solution:

def main(): print('Period of a pendulum') Earth_gravity = 9.8 Mars_gravity = 3.7263 Jupiter_gravity = 23.12 print(' ') pen = float(input('How long is the pendulum (m)? ')) if pen < 0: print('illegal length, length set to 1') else: print(' ') main()

What I want to do is if the value entered is negative for it to be set to "1" and display the message "illegal length, length set to 1" . If it is a positive number then I'll have it do the equation to find out the period of a pendulum swing. I am getting the syntax error message of " if pen < 0: builtins.NameError: name 'pen' is not defined" Thank you!

Your indentation is off. The if and else need to be indented like the rest of the function body. — interjay
– interjay, Commented Sep 16, 2017 at 21:57
@MauricioCortazar that won't help, pen is a local variable. — Alex Hall
– Alex Hall, Commented Sep 16, 2017 at 22:00

Nimish Bansal · Accepted Answer · 2017-09-16 22:00:58Z

def main(): print('Period of a pendulum') Earth_gravity = 9.8 Mars_gravity = 3.7263 Jupiter_gravity = 23.12 print(' ') pen = float(input('How long is the pendulum (m)? ')) if pen < 0: print('illegal length, length set to 1') else: print(' ') main()

Try this: pen variable was outside the function therefore it was not accesible in if statement

Just check the tick if your query is solved and if you understood your mistake :)

Eric Duminil · Accepted Answer · 2017-09-16 22:01:53Z

You first define a method in which pen is defined:

def main(): print('Period of a pendulum') Earth_gravity = 9.8 Mars_gravity = 3.7263 Jupiter_gravity = 23.12 print(' ') pen = float(input('How long is the pendulum (m)? '))

But according to the indentation, you're now trying to use pen outside of main method:

if pen < 0: print('illegal length, length set to 1') else: print(' ') main()

You can move the if/else into main method or remove the main definition altogether.

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