PythonNote001---Tricks of Python

記錄Python中常用的一些函數,備查

1 打印當前目錄

import
os


os.
getcwd()


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'/Users/liudong/There is no end to learning/[05]Learning_Python/[01]Foundation/Note of Python/[04]Tricks of Python/Code'


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2 查看幫助

1. help(os.getcwd) can help us learn more about the object
2. dir(os.getcwd) 可以幫助我們獲取該對象的大部分相關屬性
3. os.getcwd.doc為模塊、類、函數等添加說明性的文字,使程序易讀易懂,更重要的是可以通過Python自帶的標准方法將這些描述性文字信息輸出,前後各兩個下劃線

help(
os.
getcwd)


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Help on built-in function getcwd in module posix:



getcwd()

 Return a unicode string representing the current working directory.


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dir(
os.
getcwd)


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['__call__',

 '__class__',

 '__delattr__',

 '__dir__',

 '__doc__',

 '__eq__',

 '__format__',

 '__ge__',

 '__getattribute__',

 '__gt__',

 '__hash__',

 '__init__',

 '__init_subclass__',

 '__le__',

 '__lt__',

 '__module__',

 '__name__',

 '__ne__',

 '__new__',

 '__qualname__',

 '__reduce__',

 '__reduce_ex__',

 '__repr__',

 '__self__',

 '__setattr__',

 '__sizeof__',

 '__str__',

 '__subclasshook__',

 '__text_signature__']


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## 和help返回結果相同


print(
os.
getcwd.
__doc__)


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Return a unicode string representing the current working directory.


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3 列表

3.1 count of list elements

## count all elements


listA
= [
"A",
"B",
"C",
"A"]


len(
listA)


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4


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## 統計某個元素的個數


listA.
count(
"A")


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2


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## 列表增加元素


x
= [
1,
2,
3]


x.
extend([
4,
3,
2,
1])


print(
x)


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


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3.2 集合運算

## 交集


listA
= [
"A",
"B",
"C"]


listB
= [
"A",
"B",
"C",
"D"]


list(
set(
listA).
intersection(
set(
listB)))


## 或者


set(
listA)
&
set(
listB)


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{'A', 'B', 'C'}


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## 並集


list(
set(
listA).
union(
set(
listB)))


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['B', 'A', 'D', 'C']


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## 差集,在B中不在A中


list(
set(
listB).
difference(
set(
listA)))


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['D']


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3.3 列表的逆序

## 兩種方式：whether to change the original list


## 下面reverseThe flipping method will change the originallist的排序


x
=[
1,
2,
3];
y
=[
1,
2,
3]


x1
=
x[::
-
1];
y.
reverse()


print(
"now x is %s "
%
x);


print(
"x1 is %s"
%
x1);


print(
"y is %s"
%
y)


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now x is [1, 2, 3]

x1 is [3, 2, 1]

y is [3, 2, 1]


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列表排序

## sortedDoes not change the ordering of the list itself


## By assigning,完成排序


x
=[
3,
2,
1]


x1
=
sorted(
x)




## sortChange the sorting of the list itself


## The sorted data directly overwrites the original list


y
=[
3,
2,
1]


y.
sort()


y1
=
y


print(
"sorted x is %s"
%
x);


print(
"x1 is %s"
%
x1);


print(
"sorted y is %s"
%
y);


print(
"y1 is %s"
%
y1)


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sorted x is [3, 2, 1]

x1 is [1, 2, 3]

sorted y is [1, 2, 3]

y1 is [1, 2, 3]


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4 字符串

4.1 字符串截取

## Cut at equal intervals


x
=
'0123456789'


print(
x[
2:
8:
2])
# start =2 stop=10,step=2


print(
x[::
3])
## start=beginning,stop=end,sep=3


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246

0369


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5 字典

## 取出所有的key,或者所有value


x
={
'1':
'a',
'2':
'b',
'3':
'c'}


print(
list(
x.
keys()))


print(
list(
x.
values()))


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['1', '2', '3']

['a', 'b', 'c']


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6 Explanation of assignment symbols

## x,y同時綁定[1,2,3],改變x,ythe elements of a list in,內存地址id為91576392的值發生改變


x
=[
1,
2,
3]


y
=
x


y[
0]
=
3


print(
"x is %s and id is %s"
%(
x,
id(
x)))


print(
"y is %s and id is %s"
%(
y,
id(
y)))


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x is [3, 2, 3] and id is 4571010056

y is [3, 2, 3] and id is 4571010056


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7 Add module call path

## When calling a function or module,You need to add the corresponding path first


import
sys


import_path
=
"./app/python/shandaixia/stragety"


if
import_path
not
in
sys.
path:


sys.
path.
append(
import_path)


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8 文件內建函數(open)

8.1 open的基本用法

基本用法​​file_object = open(file,mode = 'r')​​ 參數含義：

1. file_nameTo open the file name string,可以是相對路徑或者是絕對路徑
2. access_modefile open model："r"讀取;"w"寫入,and for overwriting from the beginning;"a"結尾追加
3. For other parameters, please refer to the help document

8.2 文件的寫入

使用open函數,新建文本文件,進行寫入操作.

## 進行讀寫操作


f
=
open(
file
=
'test.txt',
mode
=
'w')
## 該文件不存在,Write mode auto-generated files


f.
write(
"line1 \nline2 \nline3")
## \n換行符號


f.
close()
## 關閉文件對象


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## 追加文本


f
=
open(
file
=
'test.txt',
mode
=
'a')
## 該文件不存在,Write mode auto-generated files


f.
write(
"\nline4")
## \n換行符號


f.
close()
## 關閉文件對象


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8.3 文件的讀取

Read the file content mainly divided into the function​​read​​​、​​readline​​​、​​readlines​​​.其中​​read​​​read all bytes directly into a string,​​readline​​​Read a line of data in the string,​​readlines​​Read all row data into a list,Each element in the list represents all the bytes of each row.

f
=
open(
file
=
'test.txt',
mode
=
'r')
## 讀取文件


read_txt
=
f.
read()


print(
read_txt)


f.
close()


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line1

line2

line3

line4


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## Each read reads from the end of the previous step


f
=
open(
file
=
'test.txt',
mode
=
'r')
## 讀取文件


readline_txt1
=
f.
readline()


readline_txt2
=
f.
readline()


readline_txt3
=
f.
readline()


readline_txt4
=
f.
readline()


print(
readline_txt1)


print(
readline_txt2)


print(
readline_txt3)


print(
readline_txt4)


f.
close()


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line1



line2



line3



line4


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f
=
open(
file
=
'test.txt',
mode
=
'r')
## 讀取文件


readlines_txt
=
f.
readlines()


print(
readlines_txt)


f.
close()


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['line1 \n', 'line2 \n', 'line3\n', 'line4']


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9 Find similar files in the directory

import
glob


glob.
glob(
'*.ip*')


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['Tricks of Python.ipynb']


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10 permanent storage of variables

import
pickle


f
=
open(
'somedata',
'wb')
#二進制打開 ,沒有該文件,新建


pickle.
dump([
1,
2,
3,
4],
f)
# 儲存列表


f.
close()
# 關閉文件


f
=
open(
'somedata',
'rb')
# 打開文件


x
=
pickle.
load(
f)
# 輸出變量


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[1, 2, 3, 4]


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11 向量化的ifelse

print(
'this is True')
if
1
==
1
else
print(
'this is False')


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this is True


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12 isinstance

判斷數據’123’是不是(str,int,list)one of the types

isinstance (
'123',(
str,
int,
list))


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True


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