Python Advanced (data structure and algorithm [1])

Decompose a sequence into a separate variable

>>>p = (4,5)# Decompose tuples or sequences by assigning values>>>X, y = P>>>X4>>>Y5>>>data = [' ACME ', -,91.9, ( -,1,1)]>>>Name, shares, prices, date = data>>>Name' ACME '>>>Date -,1,1)>>>Name, shares, prices, (year, month, day) = data>>>Prices91.9>>>Month1>>>Day1>>>String ="Hello" #只要对象是可迭代的, you can perform a decomposition operation>>>A, B, C, D, E = string>>>A' h '>>>B' E '>>>E' O '>>>Name, _, Prices, _ = Data#_表示不感兴趣的项>>>Name' ACME '>>>Prices91.9>>>_( -,1,1)>>>Name, _, Prices, _, outbound= data# unpacking elements do not matchTraceback (most recent): File"<pyshell#38>", line1,inch<module> name, _, Prices, _, outbound= datavalueerror:need more than4Values to unpack

Decompose elements from an arbitrary length of an iterative object

>>>*trailing, current = [ A, at, the, $, About, the, +, the]>>>Current the>>>Trailing# Use "* expression" for decomposition matching[ A, at, the, $, About, the, +]>>>A, B, *, d = [ A, the, $, About, the, the]syntaxerror:invalid syntax>>>A, B, *c, d = [ A, the, $, About, the, the]>>>A A>>>B the>>>c[ $, About, the]>>>D the>>>line =' Nobody:*:-2:user:/home '>>>uname, *others, Path = Line.split (': ')>>>Uname' Nobody '>>>Path' Home '

This is a good fit for an iterative object with a decomposition position or arbitrary length. For fixed components or patterns (for example, after element 2 is a phone number, but the number of phone numbers is unknown), using an asterisk expression can be easily and quickly decomposed.

Save last n elements

#使用collections中的deque实现From collections Import dequed = Deque () d.append (' 1 ') D.append (' 2 ') D.append (' 3 ') Len (d)# 3d[0]# 1d[-1]# 3D = deque (' 12345 ') Len (d)# 5D.popleft ()# 1D.pop ()# 5D# deque ([' 2 ', ' 3 ', ' 4 ')]#我们还可以限制deque的长度:D = deque (maxlen= -)#当限制长度的deque增加超过限制数的项时, the items on the other side are automatically deleted:D = deque (maxlen=2) D.append (1) D.append (2)# deque ([' 1 ', ' 2 '])D.append (3)# deque ([' 2 ', ' 3 '])| Append...) | Add an element to the right side of the deque.   |  | Appendleft (...) | Add an element to the left side of the deque.   |  | Clear...) | Remove all elements from the deque.   |  | Count...) | D.count (value), integer--returnNumber of occurrences of value |  | Extend...) |   Extend the right side of the deque with elements from the Iterable |  | Extendleft (...) |   Extend the left side of the deque with elements from the Iterable |  | Pop...) | Remove andreturnThe rightmost element.   |  | Popleft (...) | Remove andreturnThe leftmost element.   |  | Remove...) | D.remove (value)--Remove first occurrence of value.   |  | Reverse...) |   D.reverse ()--Reverse *in place* |  | Rotate...) | Rotate the deque n steps to the right (default n=1).      If n is negative, | Rotates left.

Python Advanced (data structure and algorithm [1])