"Basic Python Tutorial (second edition)" Learning note statements/loops/conditions (Chapter 5th)

"Basic Python Tutorial (second edition)" Learning note statements/loops/conditions (Chapter 5th)

print ' AB ', 123 ==> AB 123 # Insert a space
print ' AB ', ' CD ' ==> AB CD # Inserted a space
Print ==> 1 2 3
Print (==>) (1, 2, 3)
#在脚本中以下ABCD连在一起输出
print ' AB ',
print ' CD '

Import Somemodule #导入模块
From Somemodule import somefunction #导入函数
From Somemodule import Function1,function2 ... #导入函数
From somemodule Import *
Module1.open () #使用模块中函数
Module2.open ()
Import Math as Foobar #为模块提供别名
FOOBAR.SQRT (4)
From math import sqrt as Foobar #为函数提供别名
Foobar (4)

Sequence Unpacking
x,y,z=1,2,3; Print x, y, z ==> 1 2 3
x,y,z=1,2,3; X,y=y,z; Print x, y ==> 2 3
x=1,2,3; A,b,c=x; Print A,b,c ==> 1 2 3
d={' key1 ': ' value1 ', ' key2 ': ' value2 '}; Key,value=d.popitem (); Print Key,value ==> key2 value2

Chained assignment
x=y=z={' key1 ': ' value1 '}; X is y ==> True
x=y=z={' key1 ': ' value1 '}; X==y ==> True

Increment assignment
X+=1; X*=1;

You can indent the code with a tab or a space, and it is recommended to indent with four spaces. tab indentation is more convenient and faster than whitespace.

: Represents the beginning of a statement block

Boolean value: True, False, BOOL ()
These are seen as False:false, None, 0, "", (), [], {}
True==1 ==> True
False==0 ==> True
True+false+4 ==> 5

BOOL (' ABC ') ==> True
BOOL (") ==> False
BOOL (3) ==> True
BOOL (0) ==> False

If expression:
Block1

If expression:
Block1
Else
Block2

If expression1:
Block1
Elif expression2:
Block2
Else
Block3

Comparison operators
X==y equality operator
X!=y Unequal operators
X is y identity operator
X is not Y
The x in Y membership operator
X not in Y

0<AGE<100 # python can be used this way

' AB ' = = ' ab ' ==> True
' AB ' = = ' CD ' ==> False
12==34 ==> False

x=y=[1,2]; X==y ==> True
x=y=[1,2]; X is y ==> True
x=y=[1,2]; z=[1,2]; X is Z ==> False
x=y=[1,2]; z=[1,2]; X==z ==> True

' ABC ' < ' abc ' ==> False
[1,2]<[2,1] ==> True

Boolean operators:
And, or, not

Assertion
Age=-1; Assert 0<age<100, ' NOTE '
Traceback (most recent):
File "<pyshell#21>", line 1, in <module>
Age=-1; Assert 0<age<100, ' NOTE '
Assertionerror:note

While expression:
Block

For item in Itemset:
Block

The range function contains a lower bound and no upper limit;
Range (0,3) ==> [0, 1, 2]
Range (3) ==> [0, 1, 2]

Traverse Dictionary
d={' key1 ': ' value1 ', ' key2 ': ' value2 '};
For key in D:
Print Key,d[key]

For Key,value in D.items ():
Print Key,value

Parallel iterations
a=[1,2,3]; B=[' A ', ' B ', ' C ']; Zip (b) ==> [(1, ' a '), (2, ' B '), (3, ' C ')]

Numbering iterations
For index, string in Enumerate (strings):
If ' xxx ' in string:
strings[index]= ' NewValue '

Invert and sort iterations
Sorted ([3,1,2]) ==> [1, 2, 3]
x=[1,2,3]; List (reversed (x)) ==> [3, 2, 1] # reversed returns an iterative object

Break End Loop
Continue for the next cycle

While True:
Block1
If expression:
Break
Block2

For item in items:
Block1
If expression:
Break
Block2
Else
BLOCK3 # When the for execution is complete and no break has been performed, the BLOCK3 is executed at this time

List-derived
[X*x for X in range (3)] ==> [0, 1, 4]
[X*x for X in range (3) if x%2==0] ==> [0, 4]
[(x, Y) for x in range (3) for Y in range (3)] ==> [(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2), 1) ]

Pass # Placeholder, similar to an empty statement
Del # Delete Object
EXEC # Executes a string
EXEC "print ' abc '" ==> ABC
from math import sqrt; scope={}; exec ' sqrt=1 ' in scope; sqrt (4); scope[' sqrt '];

Eval evaluation, similar to exec
Eval (Raw_input (""))
Up
2

scope={}; scope[' x ']=2; scope[' y ']=3; Eval (' x*y ', scope) ==> 6

"Basic Python Tutorial (second edition)" Learning note statements/loops/conditions (Chapter 5th)