The following sample code illustrates how Python determines whether a variable is a local variable or a global variable:

def FtoC():
        degc = (degf - 32) / 1.8
        degk = degc + 273.15
        return degc, degk

degc = 25.3
degf = 98.6
(returnedCtemp, returnedKtemp) = FtoC()
print degc

In this code, there are actually two copies of degc: a local variable, which is used inside FtoC(), and a global variable, which has 25.3 assigned to it. The local copy of degc is created by the degc = (degf - 32) / 1.8 statement, and goes away when the function is finished. The print statement prints the value of the global variable degc, which is 25.3.

The other two rules for determining whether a variable inside a function is local or global are also illustrated by this example:

• In the degk = degc + 273.15 statement, the local variable degc is used, not the global variable of the same name. This is because the local variable is created by the preceding statement.
• In the degc = (degf - 32) / 1.8 statement, the global variable degf is used, as no local variable named degf exists.

	The best way to avoid confusion is to follow two simple guidelines when writing Python programs: Do not use a name as both a local variable and a global variable. Do not use global variables inside functions unless you absolutely have to. If you follow these guidelines, you will find it much easier to determine exactly how your functions and variables are behaving.