Some popular modules
1、sys
The module sys allows you to access variables and functions closely related to the Python interpreter.
| Function/variable | Description |
|---|---|
| argv | Command line parameters, including script name |
| exit([arg]) | Exit the current program, you can specify the return value or error message through optional parameters |
| modules | A dictionary that maps module names to loaded modules |
| path | A list containing the name of the directory in which to find the module |
| platform | A platform identifier, such as sunos5 or win32 |
| stdin | Standard input stream-an object similar to a file |
| stdout | Standard output stream-an object similar to a file |
| stderr | Standard error stream-a file-like object |
[root@li python]# vim reverseargs.py
[root@li python]# cat reverseargs.py
import sys
args = sys.argv[1:]
args.reverse()
print(' '.join(args))
[root@li python]# python3 reverseargs.py this is a test
test a is this
2
The module os allows you to access multiple operating system services.
| Function/variable | Description |
|---|---|
| about | Contains a map of environment variables |
| system(command) | Execute operating system commands in a subshell |
| sep | Separator used in the path |
| pathsep | Separator to separate different paths |
| linesep | Line separator ('\n','\r' or'\r\n') |
| urandom(n) | Returns n bytes of strongly encrypted random data |
3、fileinput
The fileinput module allows you to easily iterate over all lines in a series of text files.
| Function/variable | Description |
|---|---|
| input([files[,inplace[,backup]]]) | Help iterate over rows in multiple input streams |
| filename() | Returns the name of the current file |
| lineno () | Return (cumulative) current line number |
| filelineno () | Return the line number in the current file |
| isfirstline() | Check if the current line is the first line in the file |
| isstdin() | Check if the last line comes from sys.stdin |
| nextfile() | Close the current file and move to the next file |
| close() | Close sequence |
4. Sets, heaps, and deques
4.1, collection
The collection is implemented by the built-in class set. This means that you can create collections directly without importing classes:
>>> set(range(10))
{
0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
You can use sequences (or other iterable objects) to create collections, or you can use curly braces to explicitly specify them. Note that you cannot just use curly braces to create an empty set, as this will create a dictionary.
>>> type({
})
<class 'dict'>
The collection is mainly used for membership checking, so duplicate elements will be ignored :
>>> {
0,0,1,2,1,4,5,5,5,4}
{
0, 1, 2, 4, 5}
Like a dictionary, the order of elements in a collection is different .
In addition to membership checks, various standard set operations can be performed, such as union and intersection:
>>> a = {
1,2,3}
>>> b = {
2,3,4}
>>> a.union(b)
{
1, 2, 3, 4}
>>> a | b
{
1, 2, 3, 4}
There are some other methods and operators:
>>> c = a & b
>>> c.issubset(a)
True
>>> c <= a
True
>>> c.issuperset(a)
False
>>> c >= a
False
>>> a.intersection(b)
{
2, 3}
>>> a & b
{
2, 3}
>>> a.difference(b)
{
1}
>>> a - b
{
1}
>>> a ^ b
{
1, 4}
>>> a.copy()
{
1, 2, 3}
>>> a.copy() is a
False
Sets are mutable, so they cannot be used as dictionary keys . Another problem is that collections can only contain immutable values, so they cannot contain other collections .
>>> a = set()
>>> b = set()
>>> a.add(b)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'
The constructor forzenset creates a copy of the given set. Useful when you need to use a collection as a member of another collection or as a key in a dictionary.
4.2, heap
It is a priority queue that allows you to add objects in any order and find (and delete) the smallest element at any time . The module is named heapq.
| Function/variable | Description |
|---|---|
| heappush(heap,x) | Push x into the heap |
| heappop(heap) | Pop the smallest element from the heap |
| heapify(heap) | Let the list have heap characteristics |
| heapreolace(heap,x) | Pop the smallest element and push x into the heap |
| nlargest (n trip) | Returns the n largest elements in iter |
| nsmallest(n,iter) | Returns the n smallest elements in iter |
>>> from heapq import *
>>> from random import shuffle
>>> data = list(range(10))
>>> shuffle(data)
>>> heap = []
>>> for n in data:
... heappush(heap,n)
...
>>> heap
[0, 1, 6, 2, 4, 7, 9, 8, 3, 5]
>>> heappush(heap,0.5)
>>> heap
[0, 0.5, 6, 2, 1, 7, 9, 8, 3, 5, 4]
It is the big top heap in the data structure, that is, there is still a certain order of arrangement.
>>> heappop(heap)
0
>>> heappop(heap)
0.5
>>> heappop(heap)
1
>>> heap
[2, 3, 6, 5, 4, 7, 9, 8]
>>> heap = [5,8,0,3,6,7,9,1,4,2]
>>> heapify(heap) #就是调整堆的过程
>>> heap
[0, 1, 5, 3, 2, 7, 9, 8, 4, 6]
4.3, deque
The deque is useful when you need to delete the elements in the order they were added .
>>> from collections import deque
>>> q = deque(range(5))
>>> q.append(5)
>>> q.appendleft(6)
>>> q
deque([6, 0, 1, 2, 3, 4, 5])
>>> q.pop()
5
>>> q.popleft()
6
>>> q.rotate(3)
>>> q
deque([2, 3, 4, 0, 1])
>>> q.rotate(-1)
>>> q
deque([3, 4, 0, 1, 2])
5、time
Time module configured to obtain a current time, an operation time and date, reading time from the string, the formatted date to a string format .
| Fields in Python date tuple | ||
|---|---|---|
| index | Field | value |
| 0 | year | |
| 1 | month | 1~12 |
| 2 | day | 0~31 |
| 3 | Time | 0~23 |
| 4 | Minute | 0~59 |
| 5 | second | 0~61 |
| 6 | week | 0~6, where 0 represents Monday |
| 7 | Julian day | 1~366 |
| 8 | summer time | 0, 1 or -1 |
| Function/variable | Description |
|---|---|
| asctime([tuple]) | Convert time tuple to string |
| localtime([secs]) | Convert seconds to local time date tuple |
| mktime(tuple) | Convert time tuple to local time |
| sleep(secs) | Sleep (do nothing) secs seconds |
| strptime(string[,format]) | 将字符串转换为时间元组 |
| time() | 当前时间（从新纪元开始后的秒数） |
>>> import time
>>> time.time()
1596703340.4325356
>>> time.asctime()
'Thu Aug 6 16:42:39 2020'
6、random
模块 random 包含生成伪随机数的函数。
| 函数 | 说明 |
|---|---|
| random() | 返回一个 0~1（含）的随机数 |
| getrandbits(n) | 以长整数方式返回 n 个随机地二进制数 |
| uniform(a,b) | 返回一个 a~b（含）的随机实数 |
| randrange([start],stop,[step]) | 从 range(start,stop,step) 中随机地选择一个数 |
| choice(seq) | 从序列 seq 中随机地选择一个元素 |
| shuffle(seq[,random]) | 就地打乱序列 seq |
| sample(seq,n) | 从序列 seq 中随机地选择 n 个值不同的元素 |