The standard way is to use format string modifiers. These format string methods are available in most programming languages (via the sprintf function in c for example) and are a handy tool to know about.

To output a string of length 5:

... in Python 3.5 and above: f-strings.

i = random.randint(0, 99999)
print(f'{i:05d}')

Search for f-strings here for more details.

... Python 2.6 and above:

print '{0:05d}'.format(i)

... before Python 2.6:

print "%05d" % i

See: https://docs.python.org/3/library/string.html

You can use str.zfill:

print(str(1).zfill(2))
print(str(10).zfill(2))
print(str(100).zfill(2))

prints:

01
10
100

It's not just python it's the nature of an integer.

You can use some built in string methods to pad a string to a particular length filling with an arbitrary character like so:

>>> x = "000002"              # Set X
>>> x = int(x) + 1            # Convert X to a int and do what ever arithmetic. 
>>> print x
3
>>> x =  str(x).rjust(6,'0')  # Back to String,  Right justify padding with '0' to a length of 6
>>> print x
000003

http://docs.python.org/library/stdtypes.html#string-methods

PS. Get as familiar with string methods, and string formatting as you can, they are amazingly useful and very easy to use.

Have fun!

Try this:

str(i)