在python脚本中处理变量范围

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("==========================================")

Answer 1

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.

Answer 2

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)