Generate ID from string in Python

Question

I'm struggling a bit to generate ID of type integer for given string in Python.

I thought the built-it hash function is perfect but it appears that the IDs are too long sometimes. It's a problem since I'm limited to 64bits as maximum length.

My code so far: hash(s) % 10000000000. The input string(s) which I can expect will be in range of 12-512 chars long.

Requirements are:

integers only
generated from provided string
ideally up to 10-12 chars long (I'll have ~5 million items only)
low probability of collision..?

I would be glad if someone can provide any tips / solutions.

curious, how does this compare to things suggested here: stackoverflow.com/questions/534839/…? — Charlie Parker
– Charlie Parker, Commented Jul 25, 2022 at 19:04
why use md5 vs sha3? stackoverflow.com/questions/47601592/… — Charlie Parker
– Charlie Parker, Commented Jul 25, 2022 at 19:05
fyi you might need this: stackoverflow.com/questions/7585307/… — Charlie Parker
– Charlie Parker, Commented Jul 25, 2022 at 19:31

Stephan Kulla · Accepted Answer · 2025-09-08 12:45:06Z

19

I would do something like this:

>>> import hashlib
>>> m = hashlib.md5()
>>> m.update("some string".encode('utf-8'))
>>> str(int(m.hexdigest(), 16))[0:12]
'120665287271'

The idea:

Calculate the hash of a string with MD5 (or SHA-1 or ...) in hexadecimal form (see module hashlib)
Convert the string into an integer and reconvert it to a String with base 10 (there are just digits in the result)
Use the first 12 characters of the string.

If characters a-f are also okay, I would do m.hexdigest()[0:12].

edited Sep 8 at 12:45

answered Apr 9, 2014 at 21:50

Stephan Kulla

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9 Comments

mlen108 Over a year ago

Thanks, it looks great! It does not return integer but it just a matter of casting it back to int. Would be nice if we could go away with the int/str/int coerce dance. Any idea? :)

Stephan Kulla Over a year ago

m.hexdigit() provides a string with 32 characters. So the maximum value is 'f'*32 with 39 digits (=len(str(int('f'*32,16)))). So You can divide by 1E17 in the end. With this solution collisions might be more probably... But I did not thought it through...

Stephan Kulla Over a year ago

m.hexdigit() provides m.digest_size * 2 characters (this might change, depending on the hash function you want to use)

Stephan Kulla Over a year ago

Note: you can also use the string digest(), slice enough bytes from them and convert it to an integer (better to say: interpreting the byte string as an integer)

Gabriel Sandoval Over a year ago

I had to write "some string".encode('utf-8') instead

|

Charlie Parker · Accepted Answer · 2022-07-25 19:30:49Z

3

encode utf-8 was needed for mine to work:

def unique_name_from_str(string: str, last_idx: int = 12) -> str:
    """
    Generates a unique id name
    refs:
    - md5: https://stackoverflow.com/questions/22974499/generate-id-from-string-in-python
    - sha3: https://stackoverflow.com/questions/47601592/safest-way-to-generate-a-unique-hash
    (- guid/uiid: https://stackoverflow.com/questions/534839/how-to-create-a-guid-uuid-in-python?noredirect=1&lq=1)
    """
    import hashlib
    m = hashlib.md5()
    string = string.encode('utf-8')
    m.update(string)
    unqiue_name: str = str(int(m.hexdigest(), 16))[0:last_idx]
    return unqiue_name

see my ultimate-utils python library.

answered Jul 25, 2022 at 19:30

community wiki

Charlie Parker

Comments

Aditya · Accepted Answer · 2020-05-30 20:57:17Z

1

If you're not allowed to add extra dependency, you can continue using hash function in the following way:

>>> my_string = "whatever"
>>> str(hash(my_string))[1:13]
'460440266319'

NB:

I am ignoring 1st character as it may be the negative sign.
hash may return different values for same string, as PYTHONHASHSEED Value will change everytime you run your program. You may want to set it to some fixed value. Read here

edited May 30, 2020 at 20:57

answered May 30, 2020 at 20:29

Aditya

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