How do I join a list of integers?

Question

My code's purpose is to list all possible 4 digit numbers (0000-9999), which it does easily.

i = 0
gen = []
while i <= 9999: 
    gen.append(i)
    i = i + 1

for cycle in gen:
    format(cycle, '04')

However, it prints each number on its own line, and I would like it to print in one big string. So my question is how do I join my list of integers so that it prints in one big string? I'm running Python 3.3 on Windows.

Answer 1

So, there is a function range , which builds a generator for you; for example: range(0,10000) will generate 10,000 integers starting from 0 (0 to 9999 inclusive).

Note the range object is not a list, it's a function that will generate a list. You could make a list by doing:

list(range(0,10000))

Which gets you something like

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ... 9999]

You can use a list comprehension to format each entry in the list:

[format(x, '04') for x in range(0,10000)]

Which gives you a list of strings like:

['0000', '0001', '0002', '0003', '0004', ...

Then to join a list of strings together, there is a function called join . You want to put the empty string between each number, so you call it like this:

"".join([format(x, '04') for x in range(0,10000)])

And you get your output:

00000001000200030004000500060007 ... 9999