Python utility function Advanced (in update)

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1.pyhton Assertion

How to add an exception parameter for an ASSERT assertion statement
The exception argument to assert is to add string information after the assertion expression to explain the assertion and better know where the problem is. The format is as follows:
assert expression [, arguments]
assert expression [, parameter]

Assert Len (lists) >=5, ' list element number less than 5 '
Assert 2==1, ' 2 not equal to 1 '

2.list Complex sorting

Data_list = []  data_list.append ({' Softname ': ' 1 ', ' Version ': ' 1.2.2.2 '})  data_list.append ({' Softname ': ' 7 ', ' Version ': ' 1.2.2.2 '})  data_list.append ({' Softname ': ' 5 ', ' Version ': ' 1.2.2.2 '})  data_list.append ({' Softname ': ' 2 ', ' Version ': ' 1.2.2.2 '})  data_list.append ({' Softname ': ' 3 ', ' Version ': ' 1.2.2.2 '})  Data_ List.append ({' Softname ': ' 9 ', ' Version ': ' 1.2.2.2 '})  #升序  data_list.sort (key=lambda obj:obj.get (' Softname ') , Reverse=false)  print data_list  #[{' softname ': ' 1 '}, {' Softname ': ' 2 '}, {' Softname ': ' 3 '}, {' Softname ': ' 5 '}, { ' Softname ': ' 7 '}, {' Softname ': ' 9 '}]  #降序  data_list.sort (key=lambda obj:obj.get (' Softname '), reverse=true)  print data_list  #[{' softname ': ' 9 '}, {' Softname ': ' 7 '}, {' Softname ': ' 5 '}, {' Softname ': ' 3 '}, {' Softname ': ' 2 '}, {' Softname ': ' 1 '}]

to sort the list, Python provides two methods

Method 1: Sort by using the list's built-in function list.sort

list.sort(func=None, key=None, reverse=False)

Python instance:

>>> list = [2,5,8,9,3]    >>> list    [2,5,8,9,3]    >>> list.sort ()    >>> List    [2, 3, 5, 8, 9]

Method 2: Sort by Sequence type function sorted (list) (starting from 2.4)

Python instance:

>>> list = [2,5,8,9,3]    >>> list    [2,5,8,9,3]    >>> sorted (list)   [2, 3, 5, 8, 9]

two ways to differentiate:
Sorted (list) Returns an object that can be used as an expression. The original list does not change, creating a new sorted list object.
List.sort () does not return an object, changing the original list.
Other examples of sort:
Example 1: Forward Ordering

>>>l = [2,3,1,4]  >>>l.sort ()  >>>l  >>>[1,2,3,4]

Example 2: Reverse sorting

>>>l = [2,3,1,4]  >>>l.sort (reverse=true)  >>>l  >>>[4,3,2,1]

Example 3: Sort the second keyword

>>>l = [(' B ', 6), (' A ', 1), (' C ', 3), (' d ', 4)]   >>>l.sort (Lambda x,y:cmp (x[1],y[1]))   >> >l  >>>[(' A ', 1), (' C ', 3), (' d ', 4), (' B ', 6)]

Example 4: Sort the second keyword

>>>l = [(' B ', 6), (' A ', 1), (' C ', 3), (' d ', 4)]  >>>l.sort (key=lambda x:x[1])  >>>l  >>>[(' A ', 1), (' C ', 3), (' d ', 4), (' B ', 6)]

Example 5: Sort the second keyword

>>>l = [(' B ', 2), (' A ', 1), (' C ', 3), (' d ', 4)]  >>>import operator  >>>l.sort (key= Operator.itemgetter (1))   >>>l  >>>[(' A ', 1), (' B ', 2), (' C ', 3), (' d ', 4)]

Example 6: (DSU method: Decorate-sort-undercorate)

>>>l = [(' B ', 2), (' A ', 1), (' C ', 3), (' d ', 4)]  >>>a = [(x[1],i,x) for i,x in Enumerate (L)] #i can confirm The stable sort  >>>a.sort ()  >>>l = [s[2] for S in A] >>>l  >>>[(' A ', 1), ( ' B ', 2), (' C ', 3), (' d ', 4)]

The above gives the method of sorting the list in 6, where instance 3.4.5.6 can play an item in the list item

Sort the comparison keywords.

Efficiency comparison:

CMP < DSU < key

Comparing with the experiment, Method 3 is slower than method 6, method 6 is slower than Method 4, Method 4 and Method 5 are basically equivalent

Multi-keyword comparison sort:

Example 7:

>>>l = [(' d ', 2), (' A ', 4), (' B ', 3), (' C ', 2)]  >>> l.sort (Key=lambda x:x[1])  >>> L  >>>[(' d ', 2), (' C ', 2), (' B ', 3), (' A ', 4)]

As we can see, the sort of L is now sorted by the second keyword only,

What if we want to order the second keyword and then sort it with the first keyword? There are two ways

Example 8:

>>> L = [(' d ', 2), (' A ', 4), (' B ', 3), (' C ', 2)]  >>> l.sort (Key=lambda x: (X[1],x[0]))  >> > L  >>>[(' C ', 2), (' d ', 2), (' B ', 3), (' A ', 4)]

Example 9:

>>> L = [(' d ', 2), (' A ', 4), (' B ', 3), (' C ', 2)]  >>> l.sort (Key=operator.itemgetter (1,0))  > >> L  >>>[(' C ', 2), (' d ', 2), (' B ', 3), (' A ', 4)]  #实例8能够工作呢? The reason is that a tuple is compared from left to right, compared to the first, if equal, compare the second