Python (data structure and algorithm [1]) and python (advanced tutorial)

Python (data structure and algorithm [1]) and python (advanced tutorial)
Splits a sequence into individual variables.

>>> P = () # Break Down tuples or sequences by assigning values >>> x, y = p >>>> x4 >>> y5 >>> data = ['acme ', 50, 91.9, (, 1)] >>>> name, shares, prices, date = data >>> name 'acme '>>> date (2000, 1, 1) >>> name, shares, prices, (year, month, day) = data >>> prices91.9 >>> month1 >>>day1 >>> string = "hello" # As long as the object is iterated, you can perform the decomposition operation >>>, b, c, d, e = string >>> a'h' >>> B 'e' >>> e'o' >>>> name, _, prices, _ = data # _ items that are not interest >>>> name 'acme '>>> prices91.9 >>>_( 2000, 1, 1) >>>> name ,_, prices, _, outbound = data # The unwrapped element does not match Traceback (most recent call last): File "<pyshell #38>", line 1, in <module> name ,_, prices, _, outbound = dataValueError: need more than 4 values to unpack

Break down elements from iteratable objects of any length

>>> * Trailing, current = [12, 23, 34, 45, 56, 67, 78, 89] >>> current89 >>> trailing # use the "* expression" for decomposition and matching [12, 23, 34, 45, 56, 67, 78] >>>, b, *, d = [12, 34, 45, 56, 67,89] SyntaxError: invalid syntax> a, B, * c, d = [12, 34, 45, 56, 67,89] >>> a12 >>> b34 >>> c [45, 56, 67] >>>> d89 >>> line = 'Nobody: *:-2: user:/home '>>> uname, * others, path = line. split (':') >>> uname 'nobody' >>> path '/home'

It is no longer appropriate for iteratable objects at the decomposition position or any length. For fixed components or modes (for example, after element 2 is a phone number, but the number of phone numbers is unknown), the asterisk expression can be used for convenient and quick decomposition.

Save the last N elements

# Use deque in collections to implement from collections import dequed = deque () d. append ('1') d. append ('2') d. append ('3') len (d) # 3d [0] # 1d [-1] # 3d = deque ('000000') len (d) # 5d. popleft () # 1d. pop () # 5d # deque (['2', '3', '4']) # We can also limit the length of deque: d = deque (maxlen = 30) # When a deque with a maximum length exceeds the limit, 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 -- return number 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 and return the rightmost element. | popleft (...) | Remove and return the 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.