Python Study Notes-list

Create

 
>>> List = ["A", "B", "C", "D", "E"] >>> list ['A', 'B ', 'C', 'D', 'E']
 

Obtains an element or substring.

 
>>> List = ["A", "B", "C", "D ", "E"] # obtain the first element >>> list [0] 'A' # obtain the last element >>> list [-1] 'E' # If the index value exceeds beyond the list length,> list [10] traceback (most recent call last): file "<stdin>", line 1, in <module> indexerror: list Index out of range # Use slice to simulate the Javascript slice function and obtain the substring >>> list [] ['B', 'C ', 'D'] # The default start index of the slice is 0 >>> list [: 3] ['A', 'B ', 'C'] # The default start index of the slice is-1 >>> list [3:] ['D ', 'E'] # The length of the list is automatically corrected when the range is exceeded> list [] ['D', 'E']
 

Replace

>>> List = ["A", "B", "C", "D ", "E"] # Replace a single element >>> list [3] = "D" >>> list ['A', 'B', 'C', 'D ', 'E'] # Replace n elements >>> list [: 3] = ["A", "B", "C"] >>> list ['A ', 'B', 'C', 'D', E] # extension by replacement, a bit like JavaScript splice >>> list [-1:] = ["E", "F"] >>> list ['A', 'B', 'C', 'D', 'E ', 'F'] # shrink by replacement >>> list [-2:] = "E" >>> list ['A', 'B', 'C ', 'D', 'E']
 

Append

>>> List = ['B']

# Push an element. Note that this method does not return a value.
>>> List. append ('E ')
>>> List
>>> ['B', 'E']

# Add an element to a specified position
>>> List. insert (0, 'A ')
>>> List
['A', 'B', 'E']

# Add multiple intangible objects to a specified position
>>> List [2: 2] = ['C', 'D']
>>> List
['A', 'B', 'C', 'D', 'E']

Merge

>>> List1 = ['A', 'B', 'C'] >>> list2 = ['D ', 'E'] # Use the + operator to generate a brand new list> list3 = list1 + list2> list3 ['A', 'B', 'C ', 'D', 'E'] >>> list1 ['A', 'B', 'C'] # Use extended functions on the original list, note that this method does not return values >>> list1.extend (list2) >>> list1 ['A', 'B', 'C', 'D', 'E']
 

Detection

 
>>> List = ["A", "B", "C", "", "B"] # determine whether it is a member of the target list> "B" in listtrue> "e" in listfalse # You can use the index method to obtain location >>> list. index ("A") 0 # But an error will be reported when it is not found, shit, what is the broken design >>> list. index ("e") traceback (most recent call last): file "<stdin>", line 1, in

  
   
Valueerror: List. Index (x): x not in list

  
 

Delete

>>> List = ['A', 'B', 'C', 'C ', 'C'] # Pop functions similar to JavaScript >>> list. pop () 'B' >>> list ['A', 'B', 'C ', 'C'] # JavaScript shift function can be implemented by passing parameters >>> list. pop (0) 'A' >>> list ['A', 'A', 'B', 'C ', 'C'] # specifies the removed element. Only one element is removed at a time. >>> list. remove ('B') >>> list ['A', 'A', 'B', 'B', 'C ', 'C'] # if it does not exist, an error will be reported, which is very unfriendly >>> list. remove (10) traceback (most recent call last): file "<stdin>", line 1, in

  
   
Valueerror: list. remove (x): x not in list # Clear all 'B' elements >>> while 'B' in list: list. remove ('B')... >>> list ['A', 'A', 'C ', 'C'] # Remove a group of elements> Del list [] # Same as list [] = []> list ['A ', 'C'] # Clear all> Del list [:] # Same as list [:] = []> list []

  
 

Statistics

>>> List = ['A', 'A', 'B', 'C'] >>> Len (list) 4 # Return the number of times a appears in the list >>> list. count ('A') 2
 

List Parsing

 
>>> S = [x ** 2 for X in range (10)] >>> v = [2 ** I for I in range (13)] >>> M = [X for X in S if x % 2 = 0] >>>>> print s; print V; print M [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] [1, 2, 4, 8, 16, 32, 64,128,256,512,102 4, 2048,409 6] [0, 4, 16, 36, 64]
 

 
>>> Noprimes = [J for I in range (2, 8) for J in range (I * 2, 50, I)] >>> primes = [X for X in range (2, 50) If x not in noprimes]> Print primes [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]
 

>>> Words = 'the quick brown fox jumps over the lazy dog '. split () >>> print words [the ', 'quick', 'Brown ', 'fox', 'jumps', 'over', 'the ', 'Lazy ', 'Dog'] >>>>> stuff = [[W. upper (), W. lower (), Len (w)] for W in words] >>> for I in stuff :... print I... [The ', 'the', 3] ['quick ', 'quick', 5] ['brown ', 'Brown', 5] ['fox ', 'fox', 3] ['jumps', 'jumps', 5] ['over', 'over', 4] ['the ', 'the ', 3] ['Lazy ', 'Lazy', 4] ['Dog', 'Dog', 3] >>>>> stuff = map (lambda W: [W. upper (), W. lower (), Len (w)], words) >>> for I in stuff :... print I... [The ', 'the', 3] ['quick ', 'quick', 5] ['brown ', 'Brown', 5] ['fox ', 'fox', 3] ['jumps', 'jumps', 5] ['over', 'over', 4] ['the ', 'the ', 3] ['Lazy ', 'Lazy', 4] ['Dog', 'Dog', 3]
 

Flat a two-dimensional list

>> list = [[1, 3, 5], [2, 4] >>> [flatten for inner in list for flatten in inner] [1, 3, 5, 2, 4]