Python Tutorial– Zip, Reversed and Sorted Function

Python Exercise Lists

Python - Zip Function

The zip function is one of Python's built-in functions that can "compress" multiple sequences (lists, tuples, dictionaries, collections, strings, and lists consisting of range intervals) into a single zip object. The so-called "compression" is actually recombining the elements at the corresponding positions in these sequences to generate new tuples.

Unlike Python 3.x, the zip () function in Python 2.x returns a list directly instead of a zip object. However, the returned list or zip object contains the same elements (both tuples).

The syntax of the zip () function is:

zip (iterable, ...)

Where iterable, ... represents multiple lists, tuples, dictionaries, collections, strings, and even range intervals.

The following program demonstrates the basic usage of the zip function:

my_list = [11,12,13]
my_tuple = (21,22,23)
print([x for x in zip(my_list,my_tuple)])
my_dic = {31:2,32:4,33:5}
my_set = {41,42,43,44}
print([x for x in zip(my_dic)])
my_pychar = "python"
my_shechar = "shell"
print([x for x in zip(my_pychar,my_shechar)])
           

The output is:

[(11, 21), (12, 22), (13, 23)]
[(31,), (32,), (33,)]
[('p', 's'), ('y', 'h'), ('t', 'e'), ('h', 'l'), ('o', 'l')]

If the reader analyzes the above program and the corresponding output results, it is not difficult to find that when using the zip function to "compress" multiple sequences, it will take the first element, the second element, until n elements, each forming a new tuple. It should be noted that when the number of elements in multiple sequences is inconsistent, the shortest sequence will prevail for compression.

In addition, for the zip object returned by the zip function, you can either extract the stored tuples by traversing like the program above, or you can force the zip object into a list by calling the list function like the following program :

my_list = [11,12,13]
my_tuple = (21,22,23)
print (list (zip (my_list, my_tuple)))
           

The program execution result is:

[(11, 21), (12, 22), (13, 23)]

Python - Reversed Function

Reserved is one of the built-in functions of Python. Its function is for a given sequence (including lists, tuples, strings, and range (n) intervals). This function can return an iterator over the reversed sequence (used to traverse the Reverse sequence).

The syntax of the reserved function is as follows:

reversed (seq)

Among them, seq can be a list, an element, a string, and a list of intervals generated by range.

The following program demonstrates the basic usage of the reversed function:

#Reverse the list
print ([x for x in reversed ([1,2,3,4,5])])
#Reverse the tuples
print ([x for x in reversed ((1,2,3,4,5))])
#Reverse string
print ([x for x in reversed ("abcdefg")])
#Reverse the list of ranges generated by range ()
print ([x for x in reversed (range (10))])
           

The program execution result is:

[5, 4, 3, 2, 1]
[5, 4, 3, 2, 1]
['g', 'f', 'e', 'd', 'c', 'b', 'a']
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

In addition to using list comprehensions, you can also use the list function to directly convert the iterator returned by the reversed function into a list. Example:

#Reverse list
print (list (reversed ([1,2,3,4,5])))
           

The output is:

[5, 4, 3, 2, 1]

Again, using the reversed function to reverse the order does not modify the order of the elements in the original sequence, for example:

a = [1,2,3,4,5]
#Reverse the list
print (list (reversed (a)))
print ("a =", a)
           

The output is:

[5, 4, 3, 2, 1]
a = [1, 2, 3, 4, 5]

Python - Sorted Function

Sorted is one of Python's built-in functions that sorts sequences (lists, tuples, dictionaries, collections, and even strings).

The basic syntax of the sorted function is as follows:

list = sorted (iterable, key = None, reverse = False)

Among them, iterable indicates the specified sequence, and the key parameter can customize the collation; the reverse parameter specifies whether to sort in ascending (False, default) or descending (True) order. The sorted () function returns a sorted list.

Note that the key and reverse parameters are optional and can be used or ignored.

The following program demonstrates the basic usage of the sorted function:

#Sort the list
a = [5,3,4,2,1]
print (sorted (a))
#Sort tuples
a = (5,4,3,1,2)
print (sorted (a))
#The dictionary is sorted by key by default
a = {4: 1, \
     5: 2, \
     3: 3, \
     2: 6, \
     1: 8}
print (sorted (a.items ()))
#Sort the collection
a = {1,5,3,2,4}
print (sorted (a))
#Sort the strings
a = "51423"
print (sorted (a))
           

The program execution result is:

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]
[(1, 8), (2, 6), (3, 3), (4, 1), (5, 2)]
[1, 2, 3, 4, 5]
['1', '2', '3', '4', '5']

Again, using the sorted function to sort a sequence does not modify the original sequence, but regenerates a sorted list. Example:

a = [5,3,4,2,1] #Sort the list
print (sorted (a))
#Output the original list again a
print (a)
           

The output is:

[1, 2, 3, 4, 5]
[5, 3, 4, 2, 1]

Obviously, the sorted function does not change the sequence passed in, but returns a new, sorted list.

In addition, the sorted function sorts the elements in the sequence in ascending order by default. You can achieve descending order by manually changing its reverse parameter value to True. Example:

a = [5,3,4,2,1] #Sort the list
print (sorted (a, reverse = True))
           

The output is:

[5, 4, 3, 2, 1]

In addition, when calling the sorted function, you can also pass in a key parameter, which can accept a function whose function is to specify the criteria by which the sorted () function is sorted. Example:

chars = ['http: //http://www.freelearningpoints.com/', \
       'http: //http://www.freelearningpoints.com/python/', \
       'http: //http://www.freelearningpoints.com/shell/', \
       'http: //http://www.freelearningpoints.com/java/', \
       'http:// http://www.freelearningpoints.com/golang/']
print (sorted (chars)) #Default sort
#Custom sort by string length
print (sorted (chars, key = lambda x: len (x)))
           

The output is:

['http: //http://www.freelearningpoints.com/', 'http: //http://www.freelearningpoints.com/java/', 'http: //http://www.freelearningpoints.com/python/', 'http: //http://www.freelearningpoints.com/shell/', 'http:// http://www.freelearningpoints.com/golang/']
['http: //http://www.freelearningpoints.com/', 'http: //http://www.freelearningpoints.com/java/', 'http: //http://www.freelearningpoints.com/shell/', 'http: //http://www.freelearningpoints.com/python/', 'http:// http://www.freelearningpoints.com/golang/']