Python Course day2

First, the module

SYS Standard library

　

Import Sysprint (Sys.path)  #打印环境变量print (SYS.ARGV)

　　

Prints some paths to the storage address of the Python library.

OS Standard library

Import os# cmd_res = Os.system ("dir")  #执行命令, does not save the result cmd_res = Os.popen ("dir"). Read () print ("---->", cmd_res) Os.mkdir ("New_dir")

Third, import module

Look in the current directory first, if not, then go to the environment variable to find

Import Guess

Iv. PYC

__pycache__ Directory

When the Python program runs, the result of the compilation is saved in the Pycodeobject in memory, and when the Python program finishes running, the Python interpreter writes Pycodeobject back to the PYc file.

When the Python program runs for the second time, the program will first look for the PYc file on the hard disk, if found, compare the code time, the code time later, directly loaded, if the code time earlier than the previous process.

If not found, repeat the process above.

V. Types of data

1. Digital

A.int (integral type)

　　　　　　

Print (Type (2**32)) print (Type (2**33)) print (Type (2**50)) print (Type (2**100))

B. Float type, float

Print (Type (52.3E4)) print (Type (52.3E-4))

C. Boolean value

True or False

True or False

1 or 0

Data operations

1. Arithmetic operations:

+-*/, subtraction

% modulus, remainder

* * Power, exponentiation

The integer part that returns the quotient.

2. Comparison operation:

= =, equal to

! =, not equal to, in Python 2.x sometimes this means:<>

, <, >=, <=

3. Assignment operation

=,+=,-=,*=,/=,%=,**=,//=

4. Logical operation

And,or,not

With, or, non-

5. Member Operations

In,no in

6. Identity operations

Is,is not

A = [1,2,3,4]print (type (a)) b = Type (a) is Listprint ("B:", b) c = Type ("333") is Strprint ("C:", c) d = Type ("333") was not STRPR Int ("D:", D)

7. Bit arithmetic

&, bitwise with, and, two are all 1, take 1, other cases take 0

|, bitwise OR, or, any one of them is 1, fetch 1, other cases take 0

^, bitwise XOR, different 1, same as 0

~, bitwise reverse, first reverse (0 change to 0), minus 256

<<, move left, shift right one, multiply by 2, move right two, multiply (2*2)

>>, move right, shift right one, divide by 2, move right two, divide by (2*2)

Six or three-dollar operation

result = value 1 if condition else value 2

If the condition is true: result = value 1

If the condition is false: result = value 2

Vii.. Binary

Binary, octal, decimal, hexadecimal

Eight, bytes

Text is always Unicode, represented by the STR type, and binary data is represented by the bytes type

msg = "I love Beijing Tian ' an gate" print (msg) print (Msg.encode (encoding= "Utf-8")) Print (Msg.encode (encoding= "Utf-8"). Decode (encoding= " Utf-8 "))

　　

Python Course day2