Hi! ↵
I found python to be very easy to learn but I was not able to use it for cp before because of things like io speed which I did not know how to optimize earlier↵
these are some things I learnt which made it much easier for me to use python for cp↵
↵
Fast Input:↵
↵
~~~~~↵
import sys↵
inp = [a.strip() for a in sys.stdin.readlines()] #inp is an array of input lines.↵
~~~~~↵
↵
↵
Reading an array↵
↵
~~~~~↵
arr = [int(x) for x in inp[i].split()] # use float(x) if dealing with decimal values↵
~~~~~↵
↵
↵
↵
Making 2d matrix ( or any n dim matrix ) of 0s↵
↵
~~~~~↵
mat = [[0 for i in range(n)] for j in range(n)]↵
~~~~~↵
↵
↵
↵
Printing without the \n:↵
↵
~~~~~↵
print("output",end="")↵
~~~~~↵
↵
↵
↵
Sorting using key (see example below)↵
↵
~~~~~↵
arr = [[3,4],[1,2],[5,3],[-1,4]]↵
def fkey(a):↵
return a[0]*a[1]↵
arr.sort(key=fkey)↵
~~~~~↵
↵
↵
Reversing array/string↵
↵
~~~~~↵
arr=arr[::-1]↵
~~~~~↵
↵
↵
Note 1:↵
if arr is a list,↵
↵
~~~~~↵
brr=arr↵
brr[0]*=2 # this also modifies arr and both lists are an array of pointers to the same thing↵
~~~~~↵
↵
To make a copy of an array use this code↵
`brr=list(arr)`↵
Copy of string is also similar↵
`brr=string(arr)`↵
↵
Note 2:↵
↵
~~~~~↵
a="ilu python"↵
a[0]='a' # this line gives the following error:↵
#'str' object does not support item assignment↵
↵
# so if you have to modify the string, convert it into a list first↵
( list(a) )↵
~~~~~↵
↵
↵
Note 3: ↵
division in python normally returns a float, so to get integer division similar to cpp↵
use '//' (a//b) operator or int(a/b)↵
↵
Cpp data structures and their python equivalents:↵
↵
~~~~~↵
- vector : list↵
- Map : dict↵
- set : set↵
- string : str↵
- stack/queue: #(Implemented using list) https://www.geeksforgeeks.org/using-list-stack-queues-python/↵
- list : -↵
~~~~~↵
↵
↵
↵
Useful Libraries↵
1. Counter (to import: `from collections import Counter` ) # to count number of occurances of each element in a list↵
2. itertools (import itertools) (https://docs.python.org/2/library/itertools.html#module-itertools)↵
3. math↵
↵
Thanks!
I found python to be very easy to learn but I was not able to use it for cp before because of things like io speed which I did not know how to optimize earlier↵
these are some things I learnt which made it much easier for me to use python for cp↵
↵
Fast Input:↵
↵
~~~~~↵
import sys↵
inp = [a.strip() for a in sys.stdin.readlines()] #inp is an array of input lines.↵
~~~~~↵
↵
↵
Reading an array↵
↵
~~~~~↵
arr = [int(x) for x in inp[i].split()] # use float(x) if dealing with decimal values↵
~~~~~↵
↵
↵
↵
Making 2d matrix ( or any n dim matrix ) of 0s↵
↵
~~~~~↵
mat = [[0 for i in range(n)] for j in range(n)]↵
~~~~~↵
↵
↵
↵
Printing without the \n:↵
↵
~~~~~↵
print("output",end="")↵
~~~~~↵
↵
↵
↵
Sorting using key (see example below)↵
↵
~~~~~↵
arr = [[3,4],[1,2],[5,3],[-1,4]]↵
def fkey(a):↵
return a[0]*a[1]↵
arr.sort(key=fkey)↵
~~~~~↵
↵
↵
Reversing array/string↵
↵
~~~~~↵
arr=arr[::-1]↵
~~~~~↵
↵
↵
Note 1:↵
if arr is a list,↵
↵
~~~~~↵
brr=arr↵
brr[0]*=2 # this also modifies arr and both lists are an array of pointers to the same thing↵
~~~~~↵
↵
To make a copy of an array use this code↵
`brr=list(arr)`↵
Copy of string is also similar↵
`brr=string(arr)`↵
↵
Note 2:↵
↵
~~~~~↵
a="ilu python"↵
a[0]='a' # this line gives the following error:↵
#'str' object does not support item assignment↵
↵
# so if you have to modify the string, convert it into a list first↵
( list(a) )↵
~~~~~↵
↵
↵
Note 3: ↵
division in python normally returns a float, so to get integer division similar to cpp↵
use '//' (a//b) operator or int(a/b)↵
↵
Cpp data structures and their python equivalents:↵
↵
~~~~~↵
- vector : list↵
- Map : dict↵
- set : set↵
- string : str↵
- stack/queue: #(Implemented using list) https://www.geeksforgeeks.org/using-list-stack-queues-python/↵
- list : -↵
~~~~~↵
↵
↵
↵
Useful Libraries↵
1. Counter (to import: `from collections import Counter` ) # to count number of occurances of each element in a list↵
2. itertools (import itertools) (https://docs.python.org/2/library/itertools.html#module-itertools)↵
3. math↵
↵
Thanks!
