Variable scope in Python
Introduction[edit]
Recall that a variable is a label for a location in memory. It can be used to hold a value. In statically typed languages, variables have predetermined types, and a variable can only be used to hold values of that type. In Python, we may reuse the same variable to store values of any type.
A variable is similar to the memory functionality found in most calculators, in that it holds one value which can be retrieved many times, and that storing a new value erases the old. A variable differs from a calculator’s memory in that one can have many variables storing different values, and that each variable is referred to by name. [1]
Example of variable scope in Python[edit]
# This is a global variable
a = 0
if a == 0:
# This is still a global variable
b = 1
def my_function(c):
# this is a local variable
d = 3
print(c)
print(d)
# Now we call the function, passing the value 7 as the first and only parameter
my_function(7)
# a and b still exist
print(a)
print(b)
# c and d don't exist anymore -- these statements will give us name errors!
print(c)
print(d)
In the example above, if a user enters a string, for example 'abc', python 2.7 would throw a NameError exception. This example was swiped from the official Python documentation which you should read. [2]
# this code will generate a TypeError. We cannot concatenate a string and integer.
my_age = 16
try:
print("Your age is " + my_age)
except TypeError:
print("Hey. You should know better than to combine strings and integers!")
In the example above, we have been silly and tried to concatenate a string and an integer! We are testing for a specific type of exception, TypeError.
my_age = 16
try:
print("Your age is " + my_age)
except Exception:
print("Yikes. Something has gone horribly wrong.")
In our final example, above, we are using a generic test for any possible exception.
List of possible exceptions[edit]
Please click here for a list of exceptions