Python Learning notes 2-python file types, variables, values, strings, tuples, lists, dictionaries

Python Learning notes 2--python file types, variables, values, strings, tuples, lists, dictionaries

One, Python file type

1. Source Code

Python source code file with a. py extension, interpreted by the Pyton program, does not require compilation

[[email protected] day01]# vim 1.py#!/usr/bin/python print ' Hello world! ' [[email protected] day01]# python 1.pyhello world!

2, byte code

Python source files are compiled with a file extension of ' PYc '

Compile method:

Import Py_compile

Py_compile.compile (' hello.py ')

[Email protected] amos]$ vim 2.py#!/usr/bin/pytonimport py_compilepy_compile.compile ('./1.py ') [[email protected] day01]# vim 2.py#!/usr/bin/pythonimport py_compilepy_compile.compile (' 1.py ') [[email protected] day01]# python 2.py [[ Email protected] day01]# ls1.py 1.pyc 2.py[[email protected] day01]# python 1.pyc Hello world!

3. Optimized code

Optimized source file with "pyo" extension

-python-o-M Py_compile hello.py

[Email protected] day01]# Python-o-M py_compile 1.py[[email protected] day01]# lltotal 16-rw-r--r--. 1 root root 17:55 1.py-rw-r--r--. 1 root root 113 Feb 17:56 1.pyc-rw-r--r--. 1 root root 113 Feb 18:15 1.pyo-rw-r--r--. 1 root root 17:56 2.py[[email protected] day01]# python 1.pyohello world!

Second, Python variables

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

Python is another area of memory, and C is a re-assignment of the value of an area of memory

Name of the variable

Variable names consist of letters, numbers, underscores

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)//after discovering the new assignment A, the variable a in-memory address changes from 7601952 to 16579968

[[email protected] day01]# ipythonpython 2.6.6  (r266:84292, jul 23 2015, 15:22:56)  Type  "copyright",  "credits"  or   "License"  for more information. Ipython 1.2.1 -- an enhanced interactive python.?          -> introduction and overview of  ipython ' s features.%quickref -> quick reference.help       -> python ' S own help system.object?   -> details  about  ' object ', use  ' object?? '  for extra details. In [1]: a=123in [2]: print a123in [3]: id (a) Out[3]: 7601952In [4] :  id (a) out[4]: 7601952in [5]: a = 456in [6]: id (a) Out[6]:  16579968 

Iii. operators and expressions in Python

The Python operators include

Assignment operator x = 3,y = ' ABCD ' *=/=%= x+=2 x=x+2 x-=2 x=x-2

Arithmetic operator +-*/%//* *

Relational operators > < >= <= = = = = Return result is bool value TRUE or FALSE

Logical operator and logic with: TRUE and false or logical or FALSE or True not logical not true

Defining a variable does not need to declare the character type

in [+]: x=2in [+]: type (x) out[18]: Intin [+]: x= ' David ' in []: Type (x) out[20]: str

The arithmetic operator is simple and straightforward. 4.00//3=1.0 for rounding, 3**2=9 for 3 squared

In [£ º]: ' A ' + ' B ' out[29]: ' AB ' in [+]: 3-4out[30]: -1in []: 3*2out[31]: 6In [1In]: 4/3out[32]: []: 4.0/3out[33]: 1 .3333333333333333In []: 4.0//3OUT[34]: 1.0In []: 4.00//3OUT[35]: 1.0In []: 4%3out[36]: 1In [PNS]: 2**3out[37]: 8I n []: 3**2out[38]: 9

Relational operators

In [all]: 1>2out[39]: Falsein [MAX]: 1<9out[40]: Truein [+]: 1!=9out[41]: True

logical operators

In [all]: 1==1 and 2>1out[42]: Truein []: 1==1 and 2<1out[43]: Falsein []: 1==1 or 2<1out[44]: Truein [+]: No T 1==2out[45]: True

LAMBDA (top-down, higher priority, higher priority on the right side of the peer)

Logical operation: OR

Logical operations: and

Logical operation: not

Member Test: In,not in

Identity test: Is,is not

Comparison: <,<=,>,=>,!==,==

Bitwise OR: |

Bitwise XOR: ^

Bitwise AND: &

Shift:<<,>>

Addition and subtraction: +,-

Multiplication and division and remainder: *,/,%

Positive and negative number: +x,-x

Bitwise ROLLOVER: ~X

Index: * *

Example: writing a arithmetic device

Require a number to be read from the keyboard

[[email protected] day01]# vim 3.py#!/usr/bin/pythonnum1=input (' Please input a number ') num2=input (' please input a number ') 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) [email protected]st day01]# python 3.py Please input a number2please input a Number32+3=52-3=-12*3=62/3=0

Input () and raw_input () go:

Input () accepts numbers and strings

raw_input () resolves all to a string

in [47]: input  ("please input: ") please input: 123out[47]: 123in  [48]: input  ("please input: ") please input: abc  #这里报错, input string must be added ' ABC ' quotation marks, otherwise not recognized---------------------------------------------------------------------------nameerror                                   Traceback  (most recent  call last) <ipython-input-48-ae0272fccd43> in <module> ()----> 1  input  ("please input: ") <string> in <module> () nameerror: name  ' ABC '  is not definedIn [49]: input  ("please input: ") Please input:   ' abc ' out[49]:  ' abc ' in [50]: input  ("please input: ") Please input:  6789out[50]: 6789in [51]: raw_input  ("please input: ") please input: sdfsahfhaout[51]:   ' SDFSAHFHA ' in [52]: 234out[52]: 234in [53]: raw_input  ("Please input:   ") please input: 3242out[53]:  ' 3242 ' in [54]: raw_input  (" Please input:   ") please input: abcout[54]:  ' abc '

Iv. python data types

numeric shaping int long shaping long floating-point float (3e+7) complex -3.14j in [4]: Type (3.14j) Out[4]:complex

String three method definition string, str= ' This is a string ' str= "s is a string"

Str= ' This is a string ' ' Triple quotation mark (docstring) can be used as a comment in addition to the ability to define a string

List

Meta-group

Dictionary

Slicing operations on strings:

In [42]: a= ' ABCDE ' in [43]: aout[43]:  ' abcde ' in [44]: a[0]out[44]:  ' a ' in [45]: a[1]out[45]:  ' B ' in [46]: a[4]out[46]:  ' E ' in [47]: a[-1]out[47 ]:  ' e ' in [48]: a[0]+a[1]out[48]:  ' ab ' in [49]: a[0:2]  #取值下标注0和1, excluding the last 2out[ 49]:  ' ab ' in [50]: a[:2]out[50]:  ' ab ' in [51]: a[1:2]out[51]:  ' B ' In [52] : a[1:]out[52]:  ' bcde ' in [53]: a[:]out[53]:  ' ABCDE ' in [54]: a[-1]out[54]:   ' E ' in [55]: a[:-1]  #从头开始, excluding the last-1 corresponding eout[55]:  ' ABCD ' in [56]: a[::1]out[56 ]:  ' ABCDE ' in [57]: a[::2] #步进值为2Out [57]:  ' Ace ' in [58]: a[::-1] #步进值-1, from the back forward value out[58 ]:  ' EDCBA ' in [59]: a[::-2]out[59]:  ' ECA ' in [61]: aout[61]:  ' ABCDE ' In [ 60]: a[-4:-2]out[60]:  ' BC ' in [62]: a[-2:-4:-1]  from right to left, -2 d -3c -4b no value,- 1 = right-to-left out[62]:  ' DC ' 

An expression is a formula that joins different data (including variables, functions) with a number of operators to follow certain rules.

Assignment operators

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Python Learning notes 2-python file types, variables, values, strings, tuples, lists, dictionaries