Random string generation with upper case letters and digits

Questions : Random string generation with upper case letters and digits

How do I generate a string of size N, made of numbers and uppercase English letters such as:

  • 6U1S75
  • 4Z4UKK
  • U911K4

Total Answers: 35 Answers 35

Popular Answers:

  1. Answer in one line:

    ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(N)) 

    or even shorter starting with Python 3.6 using random.choices():

    ''.join(random.choices(string.ascii_uppercase + string.digits, k=N)) 

    A cryptographically more secure version: see this post

    ''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits) for _ in range(N)) 

    In details, with a clean function for further reuse:

    >>> import string >>> import random >>> def id_generator(size=6, chars=string.ascii_uppercase + string.digits): ...  return ''.join(random.choice(chars) for _ in range(size)) ... >>> id_generator() 'G5G74W' >>> id_generator(3, "6793YUIO") 'Y3U' 

    How does it work ?

    We import string, a module that contains sequences of common ASCII characters, and random, a module that deals with random generation.

    string.ascii_uppercase + string.digits just concatenates the list of characters representing uppercase ASCII chars and digits:

    >>> string.ascii_uppercase 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' >>> string.digits '0123456789' >>> string.ascii_uppercase + string.digits 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789' 

    Then we use a list comprehension to create a list of ‘n’ elements:

    >>> range(4) # range create a list of 'n' numbers [0, 1, 2, 3] >>> ['elem' for _ in range(4)] # we use range to create 4 times 'elem' ['elem', 'elem', 'elem', 'elem'] 

    In the example above, we use [ to create the list, but we don’t in the id_generator function so Python doesn’t create the list in memory, but generates the elements on the fly, one by one (more about this here).

    Instead of asking to create ‘n’ times the string elem, we will ask Python to create ‘n’ times a random character, picked from a sequence of characters:

    >>> random.choice("abcde") 'a' >>> random.choice("abcde") 'd' >>> random.choice("abcde") 'b' 

    Therefore random.choice(chars) for _ in range(size) really is creating a sequence of size characters. Characters that are randomly picked from chars:

    >>> [random.choice('abcde') for _ in range(3)] ['a', 'b', 'b'] >>> [random.choice('abcde') for _ in range(3)] ['e', 'b', 'e'] >>> [random.choice('abcde') for _ in range(3)] ['d', 'a', 'c'] 

    Then we just join them with an empty string so the sequence becomes a string:

    >>> ''.join(['a', 'b', 'b']) 'abb' >>> [random.choice('abcde') for _ in range(3)] ['d', 'c', 'b'] >>> ''.join(random.choice('abcde') for _ in range(3)) 'dac' 
  2. This Stack Overflow quesion is the current top Google result for “random string Python”. The current top answer is:

    ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(N)) 

    This is an excellent method, but the PRNG in random is not cryptographically secure. I assume many people researching this question will want to generate random strings for encryption or passwords. You can do this securely by making a small change in the above code:

    ''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits) for _ in range(N)) 

    Using random.SystemRandom() instead of just random uses /dev/urandom on *nix machines and CryptGenRandom() in Windows. These are cryptographically secure PRNGs. Using random.choice instead of random.SystemRandom().choice in an application that requires a secure PRNG could be potentially devastating, and given the popularity of this question, I bet that mistake has been made many times already.

    If you’re using python3.6 or above, you can use the new secrets module as mentioned in MSeifert’s answer:

    ''.join(secrets.choice(string.ascii_uppercase + string.digits) for _ in range(N)) 

    The module docs also discuss convenient ways to generate secure tokens and best practices.

  3. Simply use Python’s builtin uuid:

    If UUIDs are okay for your purposes, use the built-in uuid package.

    One Line Solution:

    import uuid; uuid.uuid4().hex.upper()[0:6]

    In Depth Version:


    import uuid uuid.uuid4() #uuid4 => full random uuid # Outputs something like: UUID('0172fc9a-1dac-4414-b88d-6b9a6feb91ea') 

    If you need exactly your format (for example, “6U1S75”), you can do it like this:

    import uuid def my_random_string(string_length=10): """Returns a random string of length string_length.""" random = str(uuid.uuid4()) # Convert UUID format to a Python string. random = random.upper() # Make all characters uppercase. random = random.replace("-","") # Remove the UUID '-'. return random[0:string_length] # Return the random string. print(my_random_string(6)) # For example, D9E50C 
  4. A simpler, faster but slightly less random way is to use random.sample instead of choosing each letter separately, If n-repetitions are allowed, enlarge your random basis by n times e.g.

    import random import string char_set = string.ascii_uppercase + string.digits print ''.join(random.sample(char_set*6, 6)) 

    Note: random.sample prevents character reuse, multiplying the size of the character set makes multiple repetitions possible, but they are still less likely then they are in a pure random choice. If we go for a string of length 6, and we pick ‘X’ as the first character, in the choice example, the odds of getting ‘X’ for the second character are the same as the odds of getting ‘X’ as the first character. In the random.sample implementation, the odds of getting ‘X’ as any subsequent character are only 6/7 the chance of getting it as the first character

  5. import uuid lowercase_str = uuid.uuid4().hex 

    lowercase_str is a random value like 'cea8b32e00934aaea8c005a35d85a5c0'

    uppercase_str = lowercase_str.upper() 

    uppercase_str is 'CEA8B32E00934AAEA8C005A35D85A5C0'

  6. From Python 3.6 on you should use the secrets module if you need it to be cryptographically secure instead of the random module (otherwise this answer is identical to the one of @Ignacio Vazquez-Abrams):

    from secrets import choice import string ''.join([choice(string.ascii_uppercase + string.digits) for _ in range(N)]) 

    One additional note: a list-comprehension is faster in the case of str.join than using a generator expression!

  7. A faster, easier and more flexible way to do this is to use the strgen module (pip install StringGenerator).

    Generate a 6-character random string with upper case letters and digits:

    >>> from strgen import StringGenerator as SG >>> SG("[ud]{6}").render() u'YZI2CI' 

    Get a unique list:

    >>> SG("[ld]{10}").render_list(5,unique=True) [u'xqqtmi1pOk', u'zmkWdUr63O', u'PGaGcPHrX2', u'6RZiUbkk2i', u'j9eIeeWgEF'] 

    Guarantee one “special” character in the string:

    >>> SG("[ld]{10}&[p]").render() u'jaYI0bcPG*0' 

    A random HTML color:

    >>> SG("#[h]{6}").render() u'#CEdFCa' 


    We need to be aware that this:

    ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(N)) 

    might not have a digit (or uppercase character) in it.

    strgen is faster in developer-time than any of the above solutions. The solution from Ignacio is the fastest run-time performing and is the right answer using the Python Standard Library. But you will hardly ever use it in that form. You will want to use SystemRandom (or fallback if not available), make sure required character sets are represented, use unicode (or not), make sure successive invocations produce a unique string, use a subset of one of the string module character classes, etc. This all requires lots more code than in the answers provided. The various attempts to generalize a solution all have limitations that strgen solves with greater brevity and expressive power using a simple template language.

    It’s on PyPI:

    pip install StringGenerator 

    Disclosure: I’m the author of the strgen module.

  8. Based on another Stack Overflow answer, Most lightweight way to create a random string and a random hexadecimal number, a better version than the accepted answer would be:

    ('%06x' % random.randrange(16**6)).upper() 

    much faster.

  9. I thought no one had answered this yet lol! But hey, here’s my own go at it:

    import random def random_alphanumeric(limit): #ascii alphabet of all alphanumerals r = (range(48, 58) + range(65, 91) + range(97, 123)) random.shuffle(r) return reduce(lambda i, s: i + chr(s), r[:random.randint(0, len(r))], "") 
  10. If you need a random string rather than a pseudo random one, you should use os.urandom as the source

    from os import urandom from itertools import islice, imap, repeat import string def rand_string(length=5): chars = set(string.ascii_uppercase + string.digits) char_gen = (c for c in imap(urandom, repeat(1)) if c in chars) return ''.join(islice(char_gen, None, length)) 
  11. This method is slightly faster, and slightly more annoying, than the random.choice() method Ignacio posted.

    It takes advantage of the nature of pseudo-random algorithms, and banks on bitwise and and shift being faster than generating a new random number for each character.

    # must be length 32 -- 5 bits -- the question didn't specify using the full set # of uppercase letters ;) _ALPHABET = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789' def generate_with_randbits(size=32): def chop(x): while x: yield x & 31 x = x >> 5 return ''.join(_ALPHABET[x] for x in chop(random.getrandbits(size * 5))).ljust(size, 'A') 

    …create a generator that takes out 5 bit numbers at a time 0..31 until none left

    …join() the results of the generator on a random number with the right bits

    With Timeit, for 32-character strings, the timing was:

    [('generate_with_random_choice', 28.92901611328125), ('generate_with_randbits', 20.0293550491333)] 

    …but for 64 character strings, randbits loses out 😉

    I would probably never use this approach in production code unless I really disliked my co-workers.

    edit: updated to suit the question (uppercase and digits only), and use bitwise operators & and >> instead of % and //

  12. Use Numpy’s random.choice() function

    import numpy as np import string if __name__ == '__main__': length = 16 a = np.random.choice(list(string.ascii_uppercase + string.digits), length) print(''.join(a)) 

    Documentation is here http://docs.scipy.org/doc/numpy-1.10.0/reference/generated/numpy.random.choice.html

  13. I’d do it this way:

    import random from string import digits, ascii_uppercase legals = digits + ascii_uppercase def rand_string(length, char_set=legals): output = '' for _ in range(length): output += random.choice(char_set) return output 

    Or just:

    def rand_string(length, char_set=legals): return ''.join( random.choice(char_set) for _ in range(length) ) 
  14. Sometimes 0 (zero) & O (letter O) can be confusing. So I use

    import uuid uuid.uuid4().hex[:6].upper().replace('0','X').replace('O','Y') 
  15. >>> import string >>> import random 

    the following logic still generates 6 character random sample

    >>> print ''.join(random.sample((string.ascii_uppercase+string.digits),6)) JT7K3Q 

    No need to multiply by 6

    >>> print ''.join(random.sample((string.ascii_uppercase+string.digits)*6,6)) TK82HK 
  16. I used this method to generate random string of length n from a -> z

    import random s = ''.join(random.choice([chr(i) for i in range(ord('a'),ord('z'))]) for _ in range(10))

  17. >>> import random >>> str = [] >>> chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890' >>> num = int(raw_input('How long do you want the string to be? ')) How long do you want the string to be? 10 >>> for k in range(1, num+1): ... str.append(random.choice(chars)) ... >>> str = "".join(str) >>> str 'tm2JUQ04CK'
  18. For those of you who enjoy functional python:

    from itertools import imap, starmap, islice, repeat from functools import partial from string import letters, digits, join from random import choice join_chars = partial(join, sep='') identity = lambda o: o def irand_seqs(symbols=join_chars((letters, digits)), length=6, join=join_chars, select=choice, breakup=islice): """ Generates an indefinite sequence of joined random symbols each of a specific length :param symbols: symbols to select, [defaults to string.letters + string.digits, digits 0 - 9, lower and upper case English letters.] :param length: the length of each sequence, [defaults to 6] :param join: method used to join selected symbol, [defaults to ''.join generating a string.] :param select: method used to select a random element from the giving population. [defaults to random.choice, which selects a single element randomly] :return: indefinite iterator generating random sequences of giving [:param length] >>> from tools import irand_seqs >>> strings = irand_seqs() >>> a = next(strings) >>> assert isinstance(a, (str, unicode)) >>> assert len(a) == 6 >>> assert next(strings) != next(strings) """ return imap(join, starmap(breakup, repeat((imap(select, repeat(symbols)), None, length)))) 

    It generates an indefinite [infinite] iterator, of joined random sequences, by first generating an indefinite sequence of randomly selected symbol from the giving pool, then breaking this sequence into length parts which is then joined, it should work with any sequence that supports getitem, by default it simply generates a random sequence of alpha numeric letters, though you can easily modify to generate other things:

    for example to generate random tuples of digits:

    >>> irand_tuples = irand_seqs(xrange(10), join=tuple) >>> next(irand_tuples) (0, 5, 5, 7, 2, 8) >>> next(irand_tuples) (3, 2, 2, 0, 3, 1) 

    if you don’t want to use next for generation you can simply make it callable:

    >>> irand_tuples = irand_seqs(xrange(10), join=tuple) >>> make_rand_tuples = partial(next, irand_tuples) >>> make_rand_tuples() (1, 6, 2, 8, 1, 9) 

    if you want to generate the sequence on the fly simply set join to identity.

    >>> irand_tuples = irand_seqs(xrange(10), join=identity) >>> selections = next(irand_tuples) >>> next(selections) 8 >>> list(selections) [6, 3, 8, 2, 2] 

    As others have mentioned if you need more security then set the appropriate select function:

    >>> from random import SystemRandom >>> rand_strs = irand_seqs(select=SystemRandom().choice) 'QsaDxQ' 

    the default selector is choice which may select the same symbol multiple times for each chunk, if instead you’d want the same member selected at most once for each chunk then, one possible usage:

    >>> from random import sample >>> irand_samples = irand_seqs(xrange(10), length=1, join=next, select=lambda pool: sample(pool, 6)) >>> next(irand_samples) [0, 9, 2, 3, 1, 6] 

    we use sample as our selector, to do the complete selection, so the chunks are actually length 1, and to join we simply call next which fetches the next completely generated chunk, granted this example seems a bit cumbersome and it is …

  19. (1) This will give you all caps and numbers:
  20. import random import string oneFile = open('‪Numbers.txt', 'w') userInput = 0 key_count = 0 value_count = 0 chars = string.ascii_uppercase + string.digits + string.punctuation for userInput in range(int(input('How many 12 digit keys do you want?'))): while key_count <= userInput: key_count += 1 number = random.randint(1, 999) key = number text = str(key) + ": " + str(''.join(random.sample(chars*6, 12))) oneFile.write(text + "n") oneFile.close()
  21. I was looking at the different answers and took time to read the documentation of secrets

    The secrets module is used for generating cryptographically strong random numbers suitable for managing data such as passwords, account authentication, security tokens, and related secrets.

    In particularly, secrets should be used in preference to the default pseudo-random number generator in the random module, which is designed for modelling and simulation, not security or cryptography.

    Looking more into what it has to offer I found a very handy function if you want to mimic an ID like Google Drive IDs:

    Return a random URL-safe text string, containing nbytes random bytes. The text is Base64 encoded, so on average each byte results in approximately 1.3 characters. If nbytes is None or not supplied, a reasonable default is used.

    Use it the following way:

    import secrets import math def id_generator(): id = secrets.token_urlsafe(math.floor(32 / 1.3)) return id print(id_generator()) 

    Output a 32 characters length id:


    I know this is slightly different from the OP’s question but I expect that it would still be helpful to many who were looking for the same use-case that I was looking for.

  22. Security Oriented Approach

    Our recommendation for anything security related is to avoid “rolling you own” and to use the secrets module which is specifically vetted for security.

    This is from the best practices section of the docs:

    import string import secrets alphabet = string.ascii_letters + string.digits password = ''.join(secrets.choice(alphabet) for i in range(8)) 

    Since you specifically asked for uppercase letters, you can either substitute ascii_uppercase for ascii_letters, or just uppercase the password with:

    password = password.upper() 

    Standard Approach Not Aiming for Security

    The canonical approach to this problem (as specified) uses the choices() function in the random module:

    >>> from random import choices >>> from string import ascii_uppercase, digits >>> population = ascii_uppercase + digits >>> str.join('', choices(population, k=6)) '6JWF1H' 
  23. import string from random import * characters = string.ascii_letters + string.punctuation + string.digits password = "".join(choice(characters) for x in range(randint(8, 16))) print password 
  24. import random q=2 o=1 list =[r'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','s','0','1','2','3','4','5','6','7','8','9','0'] while(q>o): print("") for i in range(1,128): x=random.choice(list) print(x,end="") 

    Here length of string can be changed in for loop i.e for i in range(1,length) It is simple algorithm which is easy to understand. it uses list so you can discard characters that you do not need.

  25. A simple one:

    import string import random character = string.lowercase + string.uppercase + string.digits + string.punctuation char_len = len(character) # you can specify your password length here pass_len = random.randint(10,20) password = '' for x in range(pass_len): password = password + character[random.randint(0,char_len-1)] print password 
  26. I would like to suggest you next option:

    import crypt n = 10 crypt.crypt("any sring").replace('/', '').replace('.', '').upper()[-n:-1] 

    Paranoic mode:

    import uuid import crypt n = 10 crypt.crypt(str(uuid.uuid4())).replace('/', '').replace('.', '').upper()[-n:-1] 
  27. import string, random lower = string.ascii_lowercase upper = string.ascii_uppercase digits = string.digits special = '!"£$%^&*.,@#/?' def rand_pass(l=4, u=4, d=4, s=4): p = [] [p.append(random.choice(lower)) for x in range(l)] [p.append(random.choice(upper)) for x in range(u)] [p.append(random.choice(digits)) for x in range(d)] [p.append(random.choice(special)) for x in range(s)] random.shuffle(p) return "".join(p) print(rand_pass()) # @5U,@A4yIZvnp%51 
  28. Two methods :

    import random, math 

    def randStr_1(chars:str, length:int) -> str: chars *= math.ceil(length / len(chars)) chars = letters[0:length] chars = list(chars) random.shuffle(characters) return ''.join(chars) 

    def randStr_2(chars:str, length:int) -> str: return ''.join(random.choice(chars) for i in range(chars)) 

    Benchmark :

    from timeit import timeit setup = """ import os, subprocess, time, string, random, math def randStr_1(letters:str, length:int) -> str: letters *= math.ceil(length / len(letters)) letters = letters[0:length] letters = list(letters) random.shuffle(letters) return ''.join(letters) def randStr_2(letters:str, length:int) -> str: return ''.join(random.choice(letters) for i in range(length)) """ print('Method 1 vs Method 2', ', run 10 times each.') for length in [100,1000,10000,50000,100000,500000,1000000]: print(length, 'characters:') eff1 = timeit("randStr_1(string.ascii_letters, {})".format(length), setup=setup, number=10) eff2 = timeit("randStr_2(string.ascii_letters, {})".format(length), setup=setup, number=10) print('t{}s : {}s'.format(round(eff1, 6), round(eff2, 6))) print('tratio = {} : {}n'.format(eff1/eff1, round(eff2/eff1, 2))) 

    Output :

    Method 1 vs Method 2 , run 10 times each. 100 characters: 0.001411s : 0.00179s ratio = 1.0 : 1.27 1000 characters: 0.013857s : 0.017603s ratio = 1.0 : 1.27 10000 characters: 0.13426s : 0.151169s ratio = 1.0 : 1.13 50000 characters: 0.709403s : 0.855136s ratio = 1.0 : 1.21 100000 characters: 1.360735s : 1.674584s ratio = 1.0 : 1.23 500000 characters: 6.754923s : 7.160508s ratio = 1.0 : 1.06 1000000 characters: 11.232965s : 14.223914s ratio = 1.0 : 1.27 

    The performance of first method is better.

  29. Generate random 16-byte ID containig letters, digits, ‘_’ and ‘-‘


  30. If you want an easy-to-use but highly customisable key generator, use key-generator pypi package.

    Here is the GitHub repo where you can find the complete documentation.

    You can customise it to give a string jist like you want with many more options. Here’s an example:

    from key_generator.key_generator import generate custom_key = generate(2, ['-', ':'], 3, 10, type_of_value = 'char', capital = 'mix', seed = 17).get_key() print(custom_key) # ZLFdHXIUe-ekwJCu 

    Hope this helps 🙂

    Disclaimer: This uses the key-generator library which I made.

  31. None of the answers so far guarantee presence of certain categories of characters like upper, lower, digits etc; so other answers may result in passwords that do not have digits, etc. Surprised that such a function is not part of standard lib. Here is what I use:

    def random_password(*, nchars = 7, min_nupper = 3, ndigits = 3, nspecial = 3, special=string.punctuation): letters = random.choices(string.ascii_lowercase, k=nchars) letters_upper = random.choices(string.ascii_uppercase, k=min_nupper) digits = random.choices(string.digits, k=ndigits) specials = random.choices(special, k=nspecial) password_chars = letters + letters_upper + digits + specials random.shuffle(password_chars) return ''.join(password_chars) 
  32. A random generator function without duplicates using a set to store values which have been generated before. Note this will cost some memory with very large strings or amounts and it probably will slow down a bit. The generator will stop at a given amount or when the maximum possible combinations are reached.


    #!/usr/bin/env python from typing import Generator from random import SystemRandom as RND from string import ascii_uppercase, digits def string_generator(size: int = 1, amount: int = 1) -> Generator[str, None, None]: """ Return x random strings of a fixed length. :param size: string length, defaults to 1 :type size: int, optional :param amount: amount of random strings to generate, defaults to 1 :type amount: int, optional :yield: Yield composed random string if unique :rtype: Generator[str, None, None] """ CHARS = list(ascii_uppercase + digits) LIMIT = len(CHARS) ** size count, check, string = 0, set(), '' while LIMIT > count < amount: string = ''.join(RND().choices(CHARS, k=size)) if string not in check: check.add(string) yield string count += 1 for my_count, my_string in enumerate(string_generator(6, 20)): print(my_count, my_string) 


    0 RS9N3P 1 S0GDGR 2 ZNBLFV 3 96FF97 4 38JJZ3 5 Q3214A 6 VLWNK1 7 QMT05E 8 X1ZFP0 9 MZF442 10 10L9AZ 11 GE8HIQ 12 S7PA43 13 MVLXO9 14 YX7Y0G 15 GIIKPF 16 3KCUQA 17 XHIXFV 18 BJQ5VG 19 HQF01Q 

    If your string always needs to contain letters and numbers, use this:

    #!/usr/bin/env python from typing import Generator from random import SystemRandom as RND from string import ascii_uppercase, digits def string_generator(size: int = 2, amount: int = 1) -> Generator[str, None, None]: """ Return x random strings of a fixed length. :param size: string length, defaults to 1 :type size: int, optional :param amount: amount of random strings to generate, defaults to 1 :type amount: int, optional :yield: Yield composed random string if unique :rtype: Generator[str, None, None] """ if size < 2: print( 'Since the string must contain letters and numbers,', 'its size must be at least two characters', ) return CHARS = list(ascii_uppercase + digits) LIMIT = len(CHARS) ** size count, check, string = 0, set(), '' while LIMIT > count < amount: while 1: string = ''.join(RND().choices(CHARS, k=size)) if not (string.isalpha() or string.isnumeric()): break if string not in check: check.add(string) yield string count += 1 for my_count, my_string in enumerate(string_generator(6, 20)): print(my_count, my_string) 


    0 5JIITL 1 3W7AI1 2 8QMO10 3 ETHAI8 4 BLFPP9 5 50X2CC 6 1LI8WA 7 39CKET 8 R4IM0E 9 Q3KHGS 10 65CBIU 11 XTRHO4 12 N2XIGO 13 06VFCW 14 VE9MJ8 15 A9ADHK 16 Y5ROJ0 17 OH7EJF 18 TQ709S 19 P0DDNJ 
  33. I have gone though almost all of the answers but none of them looks easier. I would suggest you to try the passgen library which is generally used to create random passwords.

    You can generate random strings of your choice of length, punctuation, digits, letters and case.

    Here’s the code for your case:

    from passgen import passgen string_length = int(input()) random_string = passgen(length=string_length, punctuation=False, digits=True, letters=True, case='upper') 
  34. I found this to be simpler and cleaner.

    str_Key = "" str_FullKey = "" str_CharacterPool = "01234ABCDEFfghij~>()" for int_I in range(64): str_Key = random.choice(str_CharacterPool) str_FullKey = str_FullKey + str_Key 

    Just change the 64 to vary the length, vary the CharacterPool to do alpha only alpha numeric or numeric only or strange characters or whatever you want.

  35. from chancepy import Chance random_string = Chance.string(length=10, pool="someLettersAndNumbers123")

Tasg: python, string