Python string-based if-statement

Question

I am writing a Python script for a project I am working on, and I am running into an error that I can't figure out. I am fairly new to Python, so I apologize if this is a very amateur question.

I have an if statement that is comparing a string that it got from a text file. it is supposed to take this input, then return a string with a file location depending on what the input was. However, when I run the script, it always resolves to the else clause, even when the input is exactly what it is being compared against.

def findfile(input):
     if input.lower() == 'option a':
          return 'file location a'
     elif input.lower() == 'option b':
          return 'file location b'
     elif input.lower() == 'option c':
          return 'file location c'
     elif input.lower() == 'option d':
          return 'file location d'
     else:
          return 'Invalid Input'

I have checks earlier in the script so that I know that the input being passed is a string. Regardless, even if I passed a string 'option b', it would return 'Invalid Input'.

Thanks in advance for any and all help!

There is a built-in function input() in Python. Do not use this name for your parameters or variables. Also, consider a dictionary lookup in {'option a' : 'file location a', ...} instead of the cascaded if. — DYZ
– DYZ, Commented Jan 24, 2017 at 23:42
Side-note: Save a little work, and perform the case conversion once, just put input = input.strip().lower() as the first line of the function, and remove the .lower() calls from each conditional test. And don't give variables the same name as Python built-ins (e.g. input) or you'll mess yourself up eventually. Perhaps inp or inputstr. — ShadowRanger
– ShadowRanger, Commented Jan 24, 2017 at 23:43
findfile('option b') returns 'file location b' so I'm guessing it isn't actually that string. — Tadhg McDonald-Jensen
– Tadhg McDonald-Jensen, Commented Jan 24, 2017 at 23:43
print is a cheap, but effective debugging tool. As the first statement of your function, put print "|" + input + "|", len(input). This will give you a solid idea of what you actually fed to the function. — Prune
– Prune, Commented Jan 24, 2017 at 23:51

Mark Ransom · Accepted Answer · 2017-01-24 23:40:54Z

2

This might happen if you get input from a file, because the string has a trailing newline. Use strip to remove it.

answered Jan 24, 2017 at 23:40

Mark Ransom

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1 Comment

Terry Jan Reedy Over a year ago

@JohnGredler Debugging with print, as suggested by Prune, would have shown the problem. This seems to be neglected in courses, but is extremely valuable to learn.

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