Set fixed length integer in python

Question

After a bit of googling, nothing came up. I am manipulating sequence numbers for network packets and need the numbers to be of a fixed length. For example:

>>> 0000 + 1
1

Instead, I'd like the integer that is returned to be 0001. Are there any built-in commands for setting an integer of fixed length?

Edit: I do not need to print these integers, I need to actually manipulate them. I will need them to iterate but they must be fixed length so that they can be easily found in a networking protocol head file.

http://stackoverflow.com/questions/339007/nicest-way-to-pad-zeroes-to-string — C.B., Nov 05 '14 at 00:30
@PadraicCunningham was assuming string length validation with int conversion. Might need more context. — C.B., Nov 05 '14 at 00:36
You can *print* the integer like this easily: `x = 1; print('{0:05d}'.format(x))`. — Marius, Nov 05 '14 at 00:38
@Ampage Grietu, the simple answer is you cannot do what you are trying to do — Padraic Cunningham, Nov 05 '14 at 00:41
Is there any reason why you can't store them as regular integers, do all the necessary manipulations keeping them as regular integers, and then when the time comes to actually display them or write them to a file, use string formatting? This still doesn't make a huge amount of sense to me. — Marius, Nov 05 '14 at 00:44
you don't send "numbers" in network packets, you send bytes. trying to do this with the numbers is barking up the wrong tree. — wim, Nov 05 '14 at 01:04

score 4 · Answer 1 · answered Nov 05 '14 at 01:00

What you're asking doesn't make any sense. The integer 0011 and the integer 11 are exactly the same number.*

If you want to format them as strings to print them out or to search a text file, you can do that with, e.g., format(n, '04'). It doesn't matter whether you're formatting 11 or 0011, they're both the same number, and that number will format to the string '0011'.

If you want to convert them to big-endian 32-bit C-style unsigned integers, again, they're both the same number, and struct.pack('>I', n) will pack that number to the byte string b'\x00\x00\x00\x0b'.

If you want to add them modulo 10000, again, they're both the same number, and (n + 9990) % 10000 will give you 1.

No matter what operation you dream up, there will be no difference.

_{* Actually, in Python 2.x, number literals starting with 0 are treated as octal, not decimal, so 0011 is actually 9, not 11. And in 3.x numbers starting with 0 are a SyntaxError, to avoid the confusion caused by accidentally writing octal numbers. But forget all that. We're not talking about the Python number literals, we're talking about something even simpler here: the numbers themselves.}

score 2 · Answer 2 · answered Nov 05 '14 at 00:58

2

Numbers don't have a "length", they're just numbers. The representation of a number as text, in a string, has a length. To convert numbers to strings in Python, use the format() function:

x = 1
s = "{:04d}".format(x)
print(s)

answered Nov 05 '14 at 00:58

Lee Daniel Crocker

12,927
3
29
55

Simpler to use the `format` function, as your text says, than the `str.format` method, as your example code does. – abarnert Nov 05 '14 at 01:02

Set fixed length integer in python

2 Answers2