How to store large integer value in value of key: value pairs of dictionary in python?

Question

I have a python dictionary of character keys and integer values. I want to store arbitrarily large integers as values of my keys. What is the maximum integer I can store as a value of my key in the dictionary? Is it possible to define the datatype of the dictionary when we initialize it? For example in C, we do map<string, long long int>. What should I do to declare the same dictionary in python?

For example, in the following code, my value will grow immensely for many keys.

 for w in words:
     ngrams_w = self.word_to_ngrams(w)
        for n in ngrams_w:
            if n in lookup_table:
                lookup_table[n] = lookup_table[n] + 1
            else:
                lookup_table[n] = 1
     return lookup_table

Now I have so many words in my corpus, resulting in too many tri-grams. So, Will the values in my lookup table be able to hold the immensely large integers?

Answer 1

Python integers can get arbitrarily large - the amount of bytes they can take up is limited only by the available memory. As a result, you can store very large integers in dicts, just like any other type of variable.

Also note that python's types are behind the scenes. The same dict can use almost anything as a key, and anything as a corresponding value. You don't need to declare it in advance.

For example:

large_dict = {
   'a': 2**99**2,
   'b': 3**99**2,
   'c': 4**66**3,
   'd': 5,
}

print(large_dict['a'])
# 24830616513292456149616454036974739771820938966442197939419359658089567202400780743905571137028486156486036903513607264042124719153572110201314197883546916952215606391372422139042592773840794323335212159700095246665013394384789465765464293679828325113232950453141468484569985222217035575296458501452872186378717438026640856834533121910412608973480242085881672164719912544082874072107422434390554486837170594217552352179217838815153995983301946373496587090616156896354994345352377952726227907079690576457293694283595586693944067261016834086680506973471228878547284373711902581003346534526356682248040411471279547066667078693613059243075566078841931213128462480543351921983621089668275721435948101887626265184182951445127840725828830209648532962314294583129458462587616879683621002666459872557839185108646816817833525155517060333482860732993614665277625489415502061774379920496929429602780585502167079135606858316403456987934488806952870800041077801533837170751376374861251329800483795256882616805854878581164361680226869833419669385928257122731195573904839938024027782370149377710658645650280419249518679276644090004956974913792951678647959778713113374754349884308332520403967474904860378939613020574276565212696855826404212709820546399167642334178336428555942563152453083892489382421641854517289230831100263608004179956903465008511600241582320500793382331980382057875456793451053160479393167189744446997815108094874623772314046414880967888630771591139242793679368373241262303020403503806741495927267535782756256226464827679171453103936982984219779689528492725634758390287762884938541414982295293195059435820985171981953652126800809143528930914867233895403413631144957773050572055247562723249843368842707168818290935719822151262157837630513192298577647355462098479363787742148415773842359155842482339588691450667863720967596151398289089712023294064255959682719606426598201025203109875583565132643670912933398263577545142697715765285834571917043394759092957857788427530930354248022105571235052694964834870559303479169142265964947215835534331232659231738844605321566863791868404356910674470711233474169254178106049934124965008926126859691353260188518891725702238011978956872340932416194028852429366663313267993063866935339039988538965602564065890425970977641916796977494816019907846068887159081996367805130377827078940214763737954464021880895504378918548182271578043448659561293769460226209756884091241789271212624443566823618854822556818054950921281495213677124939344997301596883289597036555187701021490864067003001042353911716339896584757966357696031609808169050800581900702426733604379398309018563404211559969917703040652231206637777868534421416141767113165973592413599591681134708842927135950028572565259146431359982767414698579766187600152269764793150959658673104646366308004593390529802053032008317417654941763892718192450423219923744313363894743858416682079171193877076995395458797611449453319718948222265568320631084026777091936418337638425034752

These should qualify as 'arbitrarily large integers', given that trying to print them overflows the size of my terminal window, and large_dict['c'] displays fine despite consuming about six times StackOverflow's character limit. Note that things might break when you try to convert them to floating point numbers, because those have a precision limit.

---

Python does support 'type hinting', where you can imply the type of a variable, but it doesn't actually affect anything you can do with the code. Regardless, here's how you would notate this:

# need to import Dict to type-hint about it
from typing import Dict

# hint that large_dict should use strings as keys and ints as values
# note that a 'character' is just a 1-length string, as far as python is concerned
# note also that this will not stop someone from putting a non-string in as a key, 
#   or a non-int in as a value
large_dict: Dict[str, int] = {
    ...
}