Python 3 Syntax Notation (vi) conditions, loops and asserts, pass, Del__python

Conditions:

If condition:
Statement block
Elif
Statement block
Else
Statement block

Elif represents else if

This is actually legal ... 1 < x < 2 ...

>>> if 1 < x < 2:
	print (' true ')

	
true

and represents and

>>> if x > 1 and x < 2:
	print (' true ')

	
True

or represents or

>>> x
2
>>> if x = = 2 or x = 3:
	print (x)

	
2

Returns a If B is true, otherwise it returns c A if B else c

>>> ' true ' if 1 < x <2 Else ' False '
true '

While Loop

While condition:

Statement block

Do not need parentheses oh.

>>> x
1.2
>>> while x < 2:
	print (x)
	x + + 0.2

	
1.2
1.4
1.5999999999999999
1.7999999999999998
1.9999999999999998
>>>

Often used:

While True:
    ..... If ...: Break
    ....

For Loop

For something in XXXX:

Statement block

That is, for each element in XXXX, execute some block of statements, XXXX can be a list, dictionary, tuple, iterator and so on.

>>> for x in range (0,10):
	print (x*x)

	
0
1
4
9
81

This is for.. else ... Statement
Executes only without a break, or, as long as you don't have a break, it executes

>>> for N in range (99,81,-1):
	root = sqrt (n)
	if root = Int (root):
		print (n)
break else:
	print ("I didn ' t fint it")

	
I didn ' t fint it

But you should use the list derivation as much as possible, because it's more convenient and clear

>>> [x*x for x in range (1,5)]
[1, 4, 9,]
>>> [x**2 to X in range (1,10) if x% 2 ==0]
[4, +]
>>> [(X,y) for X in range (1,3) to Y in range (4,6)]
[(1, 4), (1, 5), (2, 4), (2, 5)]

Assert assert
The following statement is true, otherwise the assertionerror appears

>>> x
1.2
>>> assert x > 1
>>> assert x > 2
traceback (most recent call L AST):
  File "<pyshell#61>", line 1, in <module>
    assert x > 2
assertionerror
>>> Assert x > 2, ' x must bigger than 2 '
traceback (most recent call last):
  File "<pyshell#64>", Line 1, in & Lt;module>
    assert x > 2, ' x must bigger than 2 '
assertionerror:x must bigger than 2

Pass

Pass means there's nothing here, no action.

If your program has unfinished functions and classes, you can add some comments, and then the Code section simply writes a pass, so that the program can run without an error, and later you can continue to refine your program

>>> class Nothing: Pass
	

del
Del deletes only the reference and the name, does not delete the value, that is, Python manages the memory automatically, is responsible for the memory recovery, this is also the python running low efficiency One reason

>>> x = [1,2,3]
>>> y = x    #x and y point to the same list
>>> del x
>>> x
traceback (most recent call last):
  File "<pyshell#41>", line 1, in <module>
    x
nameerror:name ' x ' are not de Fined
>>> y
[1, 2, 3]