The OP & accepted answer focus on formatting time, but the OP question itself discusses formatting numbers to strings in Python. In many cases, the output requires additional data fields be included along with timestamps, all of which include formatting numbers as strings.

Below are a variety of non time-based examples of formatting numbers as strings, and different ways to do so, starting with the existing string format operator (%) which has been around for as long as Python has been around (meaning this solution is compatible across Python 1.x, 2.x, and 3.x):

>>> "Name: %s, age: %d" % ('John', 35) 
'Name: John, age: 35' 
>>> i = 45 
>>> 'dec: %d/oct: %#o/hex: %#X' % (i, i, i) 
'dec: 45/oct: 055/hex: 0X2D' 
>>> "MM/DD/YY = %02d/%02d/%02d" % (12, 7, 41) 
'MM/DD/YY = 12/07/41' 
>>> 'Total with tax: $%.2f' % (13.00 * 1.0825) 
'Total with tax: $14.07' 
>>> d = {'web': 'user', 'page': 42} 
>>> 'http://xxx.yyy.zzz/%(web)s/%(page)d.html' % d 
'http://xxx.yyy.zzz/user/42.html' 

Starting in Python 2.6 (meaning it works for 2.x and 3.x), there is an alternative: the str.format() method. Here are the equivalent snippets to the above but using str.format():

>>> "Name: {0}, age: {1}".format('John', 35) 
'Name: John, age: 35' 
>>> i = 45 
>>> 'dec: {0}/oct: {0:#o}/hex: {0:#X}'.format(i) 
'dec: 45/oct: 0o55/hex: 0X2D' 
>>> "MM/DD/YY = {0:02d}/{1:02d}/{2:02d}".format(12, 7, 41) 
'MM/DD/YY = 12/07/41' 
>>> 'Total with tax: ${0:.2f}'.format(13.00 * 1.0825) 
'Total with tax: $14.07' 
>>> d = {'web': 'user', 'page': 42} 
>>> 'http://xxx.yyy.zzz/{web}/{page}.html'.format(**d) 
'http://xxx.yyy.zzz/user/42.html'

Like Python 2.6+, all Python 3 releases (so far) understand how to do both. I shamelessly ripped this stuff straight out of my hardcore Python intro book and the slides for the Intro+Intermediate Python courses I offer from time-to-time. :-)

Aug 2018 UPDATE: Of course, now that we have the f-string feature introduced in 3.6 (only works in 3.6 and newer), we need the equivalent examples of that; yes, another alternative:

>>> name, age = 'John', 35
>>> f'Name: {name}, age: {age}'
'Name: John, age: 35'

>>> i = 45
>>> f'dec: {i}/oct: {i:#o}/hex: {i:#X}'
'dec: 45/oct: 0o55/hex: 0X2D'

>>> m, d, y = 12, 7, 41
>>> f"MM/DD/YY = {m:02d}/{d:02d}/{y:02d}"
'MM/DD/YY = 12/07/41'

>>> f'Total with tax: ${13.00 * 1.0825:.2f}'
'Total with tax: $14.07'

>>> d = {'web': 'user', 'page': 42}
>>> f"http://xxx.yyy.zzz/{d['web']}/{d['page']}.html"
'http://xxx.yyy.zzz/user/42.html'

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

Try this:

str(i)

You could use the zfill function of str class. Like so -

>>> str(165).zfill(4)
'0165'

One could also do %04d etc. like the others have suggested. But I thought this is more pythonic way of doing this...