Handling variable scope in a python script

Question

I am learning to code in Python. I am creating a program that will perform unit conversions, however I have been stuck on this error for a good while:

NameError: name 'ini' is not defined

Here is the code:

a = ("Distance") b = ("Time") c = ("Volume") d = ("Temp") e = ("Weight") def conversion_type(first): if first == ("Distance"): ini = input("How great a distance am I converting?\n") elif first == ("Time"): ini = input("How much time am I converting?\n") elif first == ("Volume"): ini = input("How great a volume am I converting?\n") elif first == ("Temp"): ini = input("How many degrees am I converting?\n") elif first == ("Weight"): ini = input("How much weight am I converting?\n") else: print("That not was an afformentioned dimension you dolt.") def variable_type_converter(ini): ini = float(ini) print ("\n Welcome to the Convert-O-Matic\n==============================\n") print ("I support the following dimensions:\n") print ("%s, %s, %s, %s, and %s," % (a,b,c,d,e)) first = input("What kind of conversion would you like to do?\n") conversion_type(first) variable_type_converter(ini) print("==========================================")

I apologize, the insert code feature was spitting out garbage — John Stivers
– John Stivers, Commented Sep 14, 2015 at 1:28
@John, try again. We can always fix the formatting, especially if you leave the screenshot in there for verification (and we'll end up deleting the screenshot once the code is verified). — paxdiablo
– paxdiablo, Commented Sep 14, 2015 at 1:32
@JohnStivers Select the pasted code and then either do CTRL-k or hit the {} button. — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Sep 14, 2015 at 1:34
I came back around and typed in the code from your screenshot. I also updated my answer to note one of your functions does nothing whatsoever. — Dan Lowe
– Dan Lowe, Commented Jan 5, 2016 at 16:21

Community · Accepted Answer · 2017-05-23 11:52:23Z

ini is not declared in the global scope, only inside of functions (it is used in conversion_type() and therefore implicitly declared there, and it is an argument to variable_type_converter()). But since it was not declared in the global scope, it does not exist there. If you want to set the value of ini in conversion_type() and have the value be usable elsewhere, declare a value for ini somewhere before you call conversion_type().

This answer has a good summary of Python's scoping rules.

Update: As MadWombat points out in comments, your variable_type_converter() function doesn't do anything. It takes one argument, called ini, it casts it as float and reassigns back to ini, but then it doesn't return a value. So when the variable_type_converter() function exits, the value is discarded and and the float cast is never used.

This is a good answer. I would like to add, that by doing ini = float(ini) you are not actually converting anything. You need to return a value and assign the function result outside of the function. def to_float(ini): return float(ini) ini = to_float(ini)

djq · Accepted Answer · 2015-09-14 01:28:04Z

When defining your variables you should use a = "Distance". You should also check the conversion type using first == "Distance"

ini is not defined, is occurring because the function conversion_type(first) is returning a value that is not stored. Try:

# get conversion type conversion_type_chosen = conversion_type(first) # calculate value converted_value = variable_type_convertor(conversion_type_chosen) # print result print "result: {}".format(converted_value)

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