Too bad that Python become increasingly more
popular now, the
fastest implementation (
PyPy which nearly
as fast as Dart > Java and TCC > Crystal and NodeJS > Nim > Go) somehow
not fully compatible with the default implementation (CPython which slower than CRuby > Lua > PHP >> LuaJIT and V > PyPy). Haven't really learned about Python (and Lua) in depth (last time I learned it is about 8 years ago, same as RubyOnRails), since most of my projects can be covered with Go (backend), Ruby (scripting), Javascript (frontend), C# (games). Probably the biggest motivation to learn Python is data science (there's a bunch of libraries binding), also for LuaJIT is possibly
the fastest embeddable language (
FFI) that could bind to C easily compared to another language and
bunch of game engines that uses Lua (also have you heard
Core? it's Unity3D like game engine, that have low visibility). But this article is not about Lua, so now we'll try to learn Python, the most used stuff only (one that used in competitive programming):
Variable and
data types (int, long, string, float, bool) and structures (list, tuple, dict, set):
v1 = 1 # int or long (bigint) data type
help(v1) # list of methods and documentationsv1 = 'str' # string data type
dir(v1) # list of methods as array of string
v1 = 1.2 # float
print(v1.__doc__) # get documentation of current type or method
type(v1) == float
v1 = [1,2,'test'] # list data type
v1[-1] == 'test' # True (bool data type)
v1[::2] == [1,'test'] # step each 2
v1[:2] == [1,2] # from beginning until before index 2
v1[1:] == [2,'test'] # from index 1 until the end
range(3) == [0,1,2] # generate from range
range(1,7,2) == [1,3,5] # jump every 2
del v1[1] # delete at pos 1
any([True,1,2,3]) == True
any(['',0,False]) == False
sum([1,2,3]) == 6
v1 = [1,2,3]
v1.append(4) # changes v1 to [1,2,3,4]
v2 = v1[:] # deep copy
v1.pop() # 4
v1.remove(3) # remove first occurence
v1.insert(1,99) # changes v1 to [1,99,2]
v1.index(99) # first 99 found at position 1
v1 + v2 # [1,99,2,1,2,3,4]
v1.extend(v2) # updates v1 to ^
len(v1) # 7
i = iter(v1)
next(i) # 1
v1 = [3,2,1]
v1.sort() # v1 now [1,2,3]
v1 = (1,'test') # tuple data type
tuple([1,2,'test']) == (1,2,'test') # convert to tuple
list((1,2,'test')) == [1,2,'test'] # convert to list
v1[0] == 1 # can be indexed, but readonly
v1 += (2,) # (1,'test',2)
v1 = {'a':1, 2:3} # dict data type
list(v1) == v1.keys()
v1.values() == [1,3]
v1[4] = 5
3 in v1 # False, because no key 3 in v1
v1.get(99) == None
del v1['a']
v1 = set()
v1 = {1,2,2,1,1,3} # {1,2,3}
v1.add(3) # no effect
v1 & {1,2} # intersection
v1 | {3,4} # union
v1 - {1,2} # difference
v1 ^ {1,4} # symetric difference
v1 >= {1,2} # True if right all included in v1
v1.copy() # deep copy
Operators (arithmetic, comparison, logical, assignment, bitwise, identity/is, membership/in):
v1 / 2 # float division
v1 // 2 # integer division
v1 ** 3 # exponentiation
not (v1 > 3) # bool
v1 != 2 and v1 < 5 # bool
v1 != 2 or v1 < 5 # bool
v1 is 3 # only true when referring to same object
3 is 3 # variable with const always false
'test' + '123' # concat
v1 = '%s %d %.2f' % ('yay',1,1.2345)
v1 == 'yay 1 1.23'
v1 = '%(name)s age is %(age).2f' % {'name':'kis', 'age':34.5}
v1 == 'kis age is 34.50'
v1 = """
multi line {}
""".format('string')
v1 == '\nmulti line string\n'
'%4s' % 'a' == ' a' # 3 space before a, no need for tuple if one
int('2') == 2
float('2.34') == 2.34
str(123.456) == '123.456'
bool(0) # False, also False for '', [], {}, ()
print('yay',end='') # without newline
if 's' in v1:
print('inside')
elif '\n' in v1:
print('have newline')
else:
print('not having s or newline')
for v in v1: # only key if dict, can be iter
print(v) # can use continue or break
else:
print('only called when no break')
while True:
break
# list comprehension
[x * x for x in [1,2,3]] == [1,4,9]
[x * y for x in [1,2,3] for y in [10,20]] == [10,20,30,40,50,60]
# dict comprehension
{x:1 for x in 'abcdef' if x not in 'acf'} == {'b':1,'d':1,'e':1}
d = 0
def f1(a,b=2,c='c'):
global d # if need to modify global variable
d += 1
print(a,b,c,d) # print as tuple
f1([],3) # ([],3,'c',1)
f1 = lambda(y): y + 'test'
print(f1('a')) # atest
filter(lambda(x): x%2 == 0, [1,2,3,4,5]) == [2,4]
def f2(*a):
print(a)
f2(1,2,'a') # (1,2,'a')
def f3(**a):
print(a)
f3(x=1,y=2) # {'x':1,'y':2}
v1 = ['a','foo','ca']
v1.sort(key=lambda(x): len(x)) # sort by length
def f4(x):
return -len(x)
v1.sort(key=f4) # without lambda
class Human(object):
static_var = 10
def __init__(self):
self.name = 'kis'
def set_age(self,a):
self.age = a
def get_both(self):
return (self.name,self.age)
def static_method():
return 'whoa'
h = Human()
h.set_age(34)
print(h.get_both())
h.address = 'dzf 1/23' # create new member
del h.address
Human.static_var = 3 # all object points to this new value
h.static_var = 4 # only this object points to this new value
h2 = Human()
h2.static_var == 3 # last time changed from 10 to 3
import random
from time import clock
random.seed(clock())
v1 = random.randint(1,10) # inclusive 1 to 10
print(v1)
import math
math.sqrt(9) # 3.0
from math import ceil, floor
ceil(3.4) # 4.0
floor(3.9) # 3.0
import math as m
m.sqrt(4) # 2.0
from heapq import heappush, heappop, heapify
v1 = []
heappush(v1,4)
heappush(v1,6)
heappush(v1,5)
heappop(v1) # 4
heappop(v1) # 5
heappop(v1) # 6
v1 = [(4,'a'),(2,'b'),(1,'c'),(3,'d')]
heapify(v1) # heappop() 4 times will return sorted order
from bisect import bisect_left # C++'s lower_bound
from collections import deque
v1 = deque(v1)
v1.appendleft((1,'c'))
bisect_left(v1,(2,'b')) == 1 # returns nearest if not exists
class KV(object):
def __init__(self, l, key):
self.l = l
self.key = key
def __len__(self): # overrides len()
return len(self.l)
def __getitem__(self, index): # overrides []
return self.key(self.l[idx])
def get(self, idx):
return l[idx]
v1 = KV(v1,lambda(x): x[0])
bisect_left(v1,3)
