Tips for using python

1. Import module
The import statement is often used in Python to use objects defined in other modules (that is, other .py files).

(1). Use __name__ to write test statements
The following is a simple library program TestLib.py. When running TestLib.py directly, __name__ is "__main__". If imported, __name__ is "TestLib".

def lib_func(a):
return a + 10
def lib_func_another(b):
return b + 20
if __name__ == '__main__':
test = 101
print(lib_func(test))
print '__ name__ : ',__name__ #Pay attention to

Import the above TestLib in user.py:
import TestLib
print(TestLib.lib_func(120))

(2), more ways to use import
import TestLib as test # Quote TestLib module and rename it to t
For example:
import TestLib as t
print(t.lib_func(120))

from TestLib import lib_func # Only reference the lib_func object in TestLib and skip the TestLib reference field
This way The advantage is to reduce the memory footprint of the referenced module.
For example:
from TestLib import lib_func
print(lib_func(120))

from TestLib import * # Reference all objects in TestLib and skip the TestLib reference field
For example:
from TestLib import *
print(lib_func(120) ))

2. Query
(1), Query the parameters of the function
When we want to know which parameters a function will receive, we can use the following method to query.
import inspect
print(inspect.signature(func))

(2), query the properties of the object
In addition to using dir() to query the properties of the object, we can use the following built-in function to confirm Whether an object has a certain attribute:
hasattr(obj, attr_name) # attr_name is a string
For example:
a = [1,2,3]
print(hasattr(a,'append'))

(3 ), query the class and class name to which the object belongs
a = [1, 2, 3]
print a.__class__
print a.__class__.__name__

(4), query the parent class
We can use the __base__ attribute to query The parent class of a certain class:
cls.__base__
For example:
print(list.__base__)

3. Use Chinese (and other non-ASCII encoding)
Add #coding=utf8 in the first line of the Python program, for example:
#coding=utf8
print("How are you?")

can also be used in the following ways:
#-*- coding: UTF-8 -*-
print("How are you?")

4. Represents binary, octal and hexadecimal numbers
In versions 2.6 and above, it is expressed in the following way:
print(0b1110)   # Binary, starting with 0b
print(0o10)   # Octal, starting with 0o
print(0x2A )​​​​ # Hexadecimal, starting with 0x

If it is an earlier version, you can use the following method:

print(int("1110", 2 ))
print(int("10", 8 ))
print (int("2A", 16 ))

5. Search path
When we import, Python will look for modules in the search path. For example, the above import TestLib requires TestLib.py to be in the search path.

We can view the search path through the following method:
import sys
print(sys.path)

We can add or delete elements in sys.path while Python is running. On the other hand, we can increase the search path for Python by adding the PYTHONPATH environment variable in the shell.
Now we add /home/vamei/mylib to the search path:
$export PYTHONPATH=$PYTHONPATH:/home/vamei/mylib
You can add the front line of command to ~/.bashrc. In this way, we change the search path in the long term.

6. Combination of script and command line
You can use the following method to run a Python script. After the script is finished running, directly enter the Python command line. The advantage of this is that the script object will not be cleared and can be called directly through the command line.
$python -i script.py