You can edit py files with vim in the shell, or you can write code with pycharm, with. py as the file name

The simplest code presentation

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/13 10:15
# @Author  : eason
# @File    : FirstProgram.py

print("Hello World!")

Meaning of variables: Store temporary data while the program is running

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/13 10:15
# @Author  : eason
# @File    : FirstProgram.py


a = 3
b = a
a = 5
print(a,b)

C:\Python27\python.exe D:/worklog/pytools/s12/day1/FirstProgram.py
(5, 3)

Variables = "" must be strings here, otherwise they will be considered variables, such as

a = "alog"

a = b # If b is not defined, an error will be reported

These two are different.

a = 3
b = a
a = 5
print(a,b)

C:\Python27\python.exe D:/worklog/pytools/s12/day1/FirstProgram.py
(5, 3)

In python, it is stored as a pointer, so when b=a, b executes the corresponding data block of A. When a = 5 becomes this, the pointer of a will change, but the pointer of b will not change. In Liao Xuefeng's blog,

It's so analytic.

http://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/001374738264643de15c5c4abad47dd9510e3b86286acb8000

*******************************************************************************************************************

a = 'ABC'
b = a
a = 'XYZ'
print b

Does the last line print out the content of variable b'ABC'or'XYZ'? If we understand it mathematically, we will mistakenly conclude that B is the same as a and should also be'XYZ', but in fact the value of B is'ABC'. Let's execute the code line by line and see what happened.

Execute a ='ABC', the interpreter creates the string'ABC'and variable a, and points a to'ABC':

Executing b = a, the interpreter creates the variable b and points b to the string'ABC':

Execute a ='XYZ', the interpreter creates the string'XYZ', and changes the direction of a to'XYZ', but b does not change:

So, the result of printing variable b is naturally'ABC'.

*******************************************************************************************************************

Principles of variable naming:

1 Explicit, easy to understand
2 nums_of_alex_gf = 10
 3 NumsOfAlexGf = 2 This is called hump writing (first letter capitalized)

Write 2 and 3. Don't use two styles in your code.

Illegal naming rules

1. name-of-alex-gf = 22 can't be used - - in python it's a minus sign
 25 name = Number cannot begin
 3! Name special characters can not be!$^&*
4 name of teacher = no space
5 Some keywords cannot be declared as variables

The method to determine whether the memory address has changed, id()

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/13 10:15
# @Author  : eason
# @File    : FirstProgram.py

a = 3
print id(a)
b = a
print id(b)
a = 5
print(a,b)
print id(a)
print id(b)

C:\Python27\python.exe D:/worklog/pytools/s12/day1/FirstProgram.py
34318112
34318112
(5, 3)
34318088
34318112

In Python 3, input() corresponds to raw_input() of 2.7, and the raw_input() method has been abolished.

Judgement sentence

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/14 11:04
# @Author  : eason
# @File    : if_ext.py

sex = raw_input("input your gender:")
if sex == "girl":
    print("i wolud like to have a little monkey with tenglan")
elif sex == "man":
    print("Going to homesexual!...")
else:
    print("Pervert")

The results are as follows:

C:\Python27\python.exe D:/worklog/pytools/s12/day1/if_ext.py
input your gender:man
Going to homesexual!...

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/14 11:23
# @Author  : eason
# @File    : guest_lucknum.py.py
lucky_num = 19

input_num = raw_input("Input the guess num:")

if input_num == lucky_num:
    print("bingo!")
elif input_num > lucky_num:
    print("the real number is smaller.")
else:
    print("the real num is bigger...")

Upgraded version

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/14 11:23
# @Author  : eason
# @File    : guest_lucknum.py.py
lucky_num = 19

while True:
    input_num = int(raw_input("Input the guess num:"))

    if input_num == lucky_num:
        print("bingo!")
        break
    elif input_num > lucky_num:
        print("the real number is smaller.")
    else:
        print("the real num is bigger...")

The results obtained

C:\Python27\python.exe D:/worklog/pytools/s12/day1/guest_lucknum.py
Input the guess num:20
the real number is smaller.
Input the guess num:30
the real number is smaller.
Input the guess num:10
the real num is bigger...
Input the guess num:5
the real num is bigger...
Input the guess num:19
bingo!

Process finished with exit code 0

If break is not used, then how to deal with it?

#!/usr/bin/env python
# _*_ coding: utf-8 _*_
# @Time    : 2017/3/14 11:23
# @Author  : eason
# @File    : guest_lucknum.py.py
lucky_num = 19
input_num = -1
while lucky_num != input_num:
    input_num = int(raw_input("Input the guess num:"))
    if input_num > lucky_num:
        print("the real number is smaller.")
    elif input_num < lucky_num:
        print("the real num is bigger...")

print("Bingo!")

The results are as follows:

C:\Python27\python.exe D:/worklog/pytools/s12/day1/guest_lucknum.py
Input the guess num:20
the real number is smaller.
Input the guess num:30
the real number is smaller.
Input the guess num:10
the real num is bigger...
Input the guess num:19
Bingo!

Process finished with exit code 0