Python file types and strings

1. python file type 1. Source code--parsed directly by Python

vi 1.py  #!/usr/bin/pythonprint ‘hello world‘

Here 1.py is the source code
The execution style is similar to shell script:

• 1. After Chmod +x,./1.py
• 1. Python 1.py

2. Byte code

• Python source files are compiled and generated with the file extension PYc

• Compile method:

  [[email protected] py]# cat 2.py #!/usr/bin/pythonimport py_compile py_compile.compile(‘1.py‘)  

  Write a 2.py script, execute, the interface does not output, but look at the file list, more than a 1.PYC

  [[email protected] py]# python 2.py [[email protected] py]# ll总用量 12-rw-r--r-- 1 root root  38 12月 20 21:06 1.py-rw-r--r-- 1 root root 112 12月 20 21:10 1.pyc-rw-r--r-- 1 root root  66 12月 20 21:09 2.py

  How do you do it? or Python 2.py.
  Also, if the source file 1.py is not in, 2.py can still be executed

3. Optimizing the Code

• Optimized source files with extension pyo

• Python–o–m Py_compile 1.py

  [[email protected] py]# python -O -m py_compile 1.py[[email protected] py]# ls1.py  1.pyc  1.pyo  2.py

  After executing the optimized code, generate 1.PYO. Perform 1.pyo

  [[email protected] py]# python 1.pyohello world

Variables of 2.python

• A variable is an area of computer memory in which variables can store values within a specified range, and values can be changed.

• The python under variable is a reference to a data

• Name of the variable
  • Variable names consist of letters, numbers, and underscores.
  • Variable cannot start with a number
  • You cannot use keywords
  • A A1 _a
• Assigning values to variables
  • Is the process of declaring and defining variables
  • A = 1
  • ID (a) #id显示a在内存的位置号

In [1]: a = 123In [2]: id(a)Out[2]: 25933904In [3]: a = 456 In [4]: id(a)Out[4]: 33594056In [5]: x = ‘abc‘In [6]: x = abc ---------------------------------------------------------------------------NameError                                 Traceback (most recent call last)<ipython-input-6-c455442c5ffd> in <module>()----> 1 x = abcNameError: name ‘abc‘ is not defined

The above error explanation, by default:

数字直接写表示数字   数字带引号表示字符串   字符带引号表示字符串  字符不带引号表示变量

Python does not need to declare the type of the variable in advance and automatically determines

In [7]: a = 456In [8]: type(a)Out[8]: int

Type of variable that identifies a is an integer int

In [9]: a = ‘456‘In [10]: type(a)Out[10]: str

Type of variable that identifies a is a string str

• The Python operator includes

1. Assignment operators

=：     x = 3,   y = ‘abcd’      #等于+=：    x += 2      #x=x+2-=：    x -= 2      #x=x-2*=：    x *= 2      #x=x*2/=：    x /= 2      #x=x/2%=：    x %= 2      #取余数

2. Arithmetic operators

+-*///%**

Example 1:

In [20]: a = 1 ;b = 2In [21]: a+bOut[21]: 3In [22]: ‘a‘ + ‘b‘Out[22]: ‘ab‘

After AB assignment, A+b is a number. Add two characters directly to a string that fits together
Example 2:

In [24]: 4 / 3Out[24]: 1In [25]: 4.0 / 3Out[25]: 1.3333333333333333

4 directly except 3, because the default is an integer, so the result takes an integer 1
To get a decimal, turn 4 into a floating point number 4.0
Special,//indicates mandatory rounding

In [26]: 4.0 // 3Out[26]: 1.0

Example 3:

In [27]: 2 ** 3Out[27]: 8In [28]:  2 * 3Out[28]: 6

A * is multiply, two * * is a power

3. Relational operators

> ：    1 > 2< ：    2 < 3>=：    1 >= 1<=：    2 <= 2==：    2 == 2!=：    1 != 2

In [33]: 1 > 2Out[33]: FalseIn [34]: 1 < 2Out[34]: True

Set is true, does not set false

4. Logical operators

and逻辑与： True and Falseor逻辑或： False or Truenot逻辑非： not True

Example:

In [35]: 1 < 2 and 1 >2Out[35]: FalseIn [36]: 1 < 2 or  1 >2Out[36]: TrueIn [37]: not 1 > 2Out[37]: True

Priority order of Operations:

• Input and Raw_input
  Input suitable for numbers, raw_input for characters

In [41]: input("input num:")input num:123Out[41]: 123In [42]: input("input num:")input num:abc---------------------------------------------------------------------------NameError                                 Traceback (most recent call last)<ipython-input-42-3cd60768312e> in <module>()----> 1 input("input num:")<string> in <module>()NameError: name ‘abc‘ is not definedIn [43]: input("input num:")input num:‘abc‘Out[43]: ‘abc‘In [44]: raw_input("input num:")input num:abcOut[44]: ‘abc‘

There can be seen above in input, direct input ABC error, but raw_input normal display.
This allows you to write a calculation script

!/sur/bin/python

NUM1 = input ("Please input a num:")

num2 = input ("Please input a num:")

Print "%s +%s =%s"% (NUM1,NUM2,NUM1+NUM2)

Print "%s-%s =%s"% (NUM1,NUM2,NUM1-NUM2)

Print "%s *%s =%s"% (NUM1,NUM2,NUM1*NUM2)

Print "%s/%s =%s"% (NUM1,NUM2,NUM1/NUM2)

%s分别对应后面的数值  执行脚本

[email protected] py]# python cal.py
Please input a num:5
Please input a num:6
5 + 6 = 11
5-6 = 1
5 * 6 = 30
5/6 = 0

### 3.Python的数值和字符串数值类型：    - [ ] 整形int  整型int可以存储2^32个数字，范围-2,147,483,648到2147483647      例如：0，100，-100- [ ] 长整型long  Long的范围很大，几乎可以说任意大的整数均可以存储。  为了区分普通整型，需要在整数后加L或l。   例如： 2345L，0x34al  - [ ] 浮点float  例如：0.0，12.0，-18.8，3e+7等- [ ] 复数型complex  Python对复数提供内嵌支持，这是其他大部分软件所没有的。  复数例子：- 3.14j，8.32e-36j     - [ ] 字符串 string     有三种方法定义字符串类型    - str = ‘this is a string’ #普通字符串    - str = “this is a string”  #能够解析\n等特殊字符    - str = ‘’‘this is a string’‘’  #可以略去\n  三重引号（docstring）除了能定义字符串还可以用作注释。  举例：  

In [3]: a = "' Hello"
...: World "

In [4]: A
OUT[4]: ' Hello\nworld '

In [5]: Print a
Hello
World

- 字符串索引，0开始，-1表示最后一个，-2倒数第二个，类推

In [6]: a = ' ABCDE '

In [7]: A[0:2]
OUT[7]: ' AB '

a[]表示取索引指定的字符，[0:2]可以类比数学中的0<=a<2，即0<=a<=1，就是取第一个和第二个，不包括第三个

In [8]: A[:2]
OUT[8]: ' AB '

In [9]: a[:]
OUT[9]: ' ABCDE '

0或者-1可以省略  - 字符串切片  

In [all]: A[0:3:2]
OUT[11]: ' AC '

只取a和c，首先应该是a[0:3]，但是这样的结果是abc，a[0:3:2]的2表示步进2个，跳过b。同理，如果是a[0:3:3]表示步进3。    **如果要将整个字符串倒过来，需要用-1  

In []: A[::-1]
OUT[17]: ' EDCBA '

可以类比下面的

in [+]: a[:-1]
OUT[16]: ' ABCD '

来个更加直观的

In []: A[-2:-4:-1]
OUT[13]: ' DC '

取倒数第2个和倒数第三个，而且倒序显示### 4.作业

Convert "123" to an integer
Convert "9999999999999999999" to grow integer
Convert "3.1415926" to a floating-point number
Convert 123 to a string
The following string exists
String 1: "ABC defgh&IJKL opq mnrst (uvwxyz"
String 2: "Abc#def gh%ij mnopq klrs&&tuvwx (&yz")
Various methods of using strings are converted into the following ways
Abcdefghijklmnopqrstuvwxyzzyxwvutsrqponmlkjihgfedcba

解答：  1.将 “123” 转换成整数

num = Int (123)
Print num

2.将 “9999999999999999999” 转换成长整数

num = Long (9999999999999999999)
Print num

3.将 “3.1415926” 转换成一个浮点数

num = float (3.1415926)
Print num

4.将 123 转换成一个字符串

num = str (123)
Print num

5.最后一题  分析思路：两个字符串都要剔除首尾空格，特殊字符，转换大小写，切片，相加  - [ ] 剔除首尾空格，特殊字符

STR1 = "ABC defgh&IJKL opq mnrst ((uvwxyz"
str2 = "Abc#def gh%ij mnopq klrs&&tuvwx (&yz")
STR1 = Str1.strip ()
STR2 = Str2.strip ()
Print str1
Print str2

strip()剔除首尾分隔符，默认是空格，可以自定义，自定义用‘XX‘例子见图示     ![](http://os9ep64t2.bkt.clouddn.com/17-12-20/90753838.jpg)  执行结果

C:\Users\chawn\PycharmProjects\171220\venv\Scripts\python.exe c:/users/chawn/. pycharmce2017.3/config/scratches/scratch.py
ABC defgh&IJKL opq Mnrst (uvwxyz
Abc#def gh%ij mnopq klrs&&tuvwx (&yz

还可以用替换来剔除空格、其他字符

STR1 = "ABC defgh&IJKL opq mnrst ((uvwxyz"
str2 = "Abc#def gh%ij mnopq klrs&&tuvwx (&yz")
STR1 = Str1.replace (","). Replace (' &', '). Replace (' (' (') ' (')
STR2 = Str2.replace (","). Replace (' # ', '). Replace ('% ', '). Replace (' && ', '). Replace (' (& ', ')

Print str1
Print str2

replace可以替换任意位置的空格，还有字符  - [ ] 大小写转换+切片

STR1 = "ABC defgh&IJKL opq mnrst ((uvwxyz"
str2 = "Abc#def gh%ij mnopq klrs&&tuvwx (&yz")
STR1 = Str1.replace (","). Replace (' &', '). Replace (' (' (') ' (')
STR2 = Str2.replace (","). Replace (' # ', '). Replace ('% ', '). Replace (' && ', '). Replace (' (& ', ')
STR1 = Str1.lower ()
STR1 = str1[0:12]+str1[15:17]+str1[12:15]+str1[17:]
STR2 = str2[0:10]+str2[10:15]+str2[15:17]+str2[17:]
Print str2 + str1[::-1]

执行结果  

C:\Users\chawn\PycharmProjects\171220\venv\Scripts\python.exe c:/users/chawn/. pycharmce2017.3/config/scratches/scratch.py
Abcdefghijmnopqklrstuvwxyzzyxwvutsrqponmlkjihgfedcba
```

Python file types and strings