python之基础

python之基础

1. Simple expression

[python]
3e-10    #10的－10次  
10//3     #10/3的整数部分  
10%3    #余数 

3e-10    #10的－10次
10//3     #10/3的整数部分
10%3    #余数

2.Sets

[python]
<SPAN style="FONT-SIZE: 10px">x = {}   #dictionary not set  
x = set()  #set  
sum({1,2,3}) 
sum({1,2,3}, 3) 
 
num = {1,2,3} 
2 in num #return True  
2 not in num #return False  
 
{1,2,3} | {3,4,5}  #set union  
{1,2} & {1,2,3}   # set intersection  
 
S = {1,2,3} 
S.add(4)   #add element  
S.remove(2) #remove element  
S.update({4,5,6}) #the argument should be set  
S.intersection_update({5,6,7,8}) 
 
U = S.copy() #we can copy S to U in order to avoid operating S  
 
{2*x for x <SPAN style="FONT-FAMILY: Arial, Helvetica, sans-serif">in  {1,2,3}}  #set comprehension</SPAN>  
 
S = {1, 2, 3, 4} 
T = {3, 4, 5, 6} 
S_intersect_T = { x for x in S for y in T if x == y }      #intersect using set comprehension</SPAN> 

x = {}   #dictionary not set
x = set()  #set
sum({1,2,3})
sum({1,2,3}, 3)

num = {1,2,3}
2 in num #return True
2 not in num #return False

{1,2,3} | {3,4,5}  #set union
{1,2} & {1,2,3}   # set intersection

S = {1,2,3}
S.add(4)   #add element
S.remove(2) #remove element
S.update({4,5,6}) #the argument should be set
S.intersection_update({5,6,7,8})

U = S.copy() #we can copy S to U in order to avoid operating S

{2*x for x in  {1,2,3}}  #set comprehension

S = {1, 2, 3, 4}
T = {3, 4, 5, 6}
S_intersect_T = { x for x in S for y in T if x == y }      #intersect using set comprehension

 

3.Lists

[python]
L = list() #2 kinds of list initialization  
L = [] 
L = [1,2,3] 
sum(L) 
[1,2,3] + ['a','b'] 
 
dictionary = {1:'a', 2:'b'} 
L = list(dictionary)   # the entries of list is the keys of dictionary  
 
L[1] #obtaining elements of a list by indexing  
L[1:10] # obtaining elements (index 1 to 10)  
L[1:10:2] # return [1,3,5,7,9]  
 
L.append(x) # add x to the end of the list  
L.pop(i)   #delete the ith element and return the remainder 

L = list() #2 kinds of list initialization
L = []
L = [1,2,3]
sum(L)
[1,2,3] + ['a','b']

dictionary = {1:'a', 2:'b'}
L = list(dictionary)   # the entries of list is the keys of dictionary

L[1] #obtaining elements of a list by indexing
L[1:10] # obtaining elements (index 1 to 10)
L[1:10:2] # return [1,3,5,7,9]

L.append(x) # add x to the end of the list
L.pop(i)   #delete the ith element and return the remainder

 

4.Dictionary

[python]
<SPAN style="FONT-SIZE: 10px">d = {} # initialization  
d = dict() 
{1:2, 1:3}  #return {1:3}  
 
square_dict = {i:i**2 for i in range(100)} 
 
d = {1:1, 2:2} 
1 in d   #return True    p.s. do not use .has_key() since it is no longer used in Python 3.x  
1 in d.keys()  # return True  
 
d.items()   
d.values() 
d.keys()</SPAN> 

d = {} # initialization
d = dict()
{1:2, 1:3}  #return {1:3}

square_dict = {i:i**2 for i in range(100)}

d = {1:1, 2:2}
1 in d   #return True    p.s. do not use .has_key() since it is no longer used in Python 3.x
1 in d.keys()  # return True

d.items() 
d.values()
d.keys()

5.Others

[python]
list(range(3)) #return [0, 1, 2] 3 is not included  
list(zip([1,2,3], [2,3,4])) # return[(1, 2), (2, 3), (3, 4)] 

list(range(3)) #return [0, 1, 2] 3 is not included
list(zip([1,2,3], [2,3,4])) # return[(1, 2), (2, 3), (3, 4)]