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, Sep 14 '15 at 01:28
@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, Sep 14 '15 at 01:32
@JohnStivers Select the pasted code and then either do CTRL-k or hit the `{}` button. — Ashwini Chaudhary, Sep 14 '15 at 01:34
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, Jan 05 '16 at 16:21

score 2 · Accepted Answer · edited May 23 '17 at 11:52

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) — Mad Wombat, Jan 05 '16 at 16:11

score 1 · Answer 2 · answered Sep 14 '15 at 01:28

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)

Handling variable scope in a python script

2 Answers2