Python i.e. true non-empty, the list formula, ternary expressions day3

First, that is non-empty true:

Python programming language specify any non-empty and non-0 (null) is true, 0 is false, or null

1. Boolean, False representation False, the other is True
2. Integer and floating-point numbers, 0 for False, the other is True
3. String String type and class (including bytes and unicode), empty string indicates False, the other is True
4. Sequence type (including tuple, list, dict, set, etc.), empty indicates False, True indicates a non-empty
5. None always expressed False

Example a: 
S = '' 
IF S:
     Print ( ' walking IF ' )
 else :
     Print ( " go else " )   # go else 
Example II: 
username = INPUT ( ' username: ' )
 IF username:
     Print ( " User name is S% " % username) # If you enter a name to go IF 
else :
     Print ( " Please enter your user name " ) # If you enter a user name to go else 
example III: 
A= 0

if a :
    print("go if")
else:
    print("go else")#走else

Second, the list of formula:

python inside [] represents a list, the list can be used to quickly generate a range () function is generated.
Inside the list of data operations and operations to generate a new list of the most efficient and rapid way, that is the formula list generation.

 1、range()

A sequential list of numeric type, such as [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], can be used to generate range

= b the Range (1, 11 )
 Print (b)   # result range (1, 11) python3 direct printing b displays range (1, 11) objects should not directly display the list, if you want to display a list, you can use list ( ) on the next 
Print (type (B)) # results <class 'Range'> 
Print (List (B)) # turn List, output is [1, 2, 3, 4, 5, 6, 7, 8, 9 , 10]

2, a list of formula

(1). If you want to regenerate the data of the list which calculates a new list, such as [11, 2 2 33  ... 1010 ], according to the usual definition of a list of thinking is C, then one by one for loop operation , and then append a goner Add to c, c is the last of the new list

# Logarithm of the square of the list 

B = Range (1. 11 ) 
C = []
 for I in B: 
    c.append (I * I)
 Print (C) 

# Results: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

(2) Next to see a list of how to achieve the formula

# Log listing squares 

B = Range (1. 11 ) 
C = [X * X for X in B]
 Print (C) 

# Results: [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

(3) a list of fixed syntax formula, [] which is in front of arithmetic operation for the inside data list, followed sequentially as usual for traversing to read. It will automatically generate a new list after running

3, if the judge with

1. If you want to filter data inside a list, for example: [1, 3, -3, 4, -2, 8, -7, 6], to find the number is greater than 0 and to be one by one for normal cycle thinking Analyzing , qualified into a new list

= C [. 1,. 3, -3,. 4, -2,. 8, -7,. 6] 
D = [] 
for I in C: 
    IF I> 0: 
        d.append (I) added to the list # D 
Print (D ) 

# results: [1, 3, 4, 8, 6]

2. Next you can see a list of the formula, write code more simple and elegant, fast and efficient!

# Extracted number greater than 0 
C = [1,. 3, -3,. 4, -2,. 8, -7,. 6 ] 
D = [X for X in C IF X> 0]
 Print (D) 

# Run Results [1 , 3, 4, 8, 6]

Another example:

= result3 [STR (I +. 1) .zfill (2) for I in Range (1,10 )]
 Print (result3)
 # Ê equivalent 
result4 = []
 for I in Range (1,10 ): 
    J = STR (I +. 1) .zfill (2 ) 
    result4.append (J) 
Print (result4) # print the results [ '01', '02', '03', '04', '05', '06', ' 07 ',' 08 ',' 09 ']

Third, a triplet of expressions

# Ternary expressions with 
# ID 17 bits represent gender, male odd, even-F 
id_card = ' 211105200103052312 ' 

IF int (id_card [-2])% 2 == 0: 
    Sex = ' F ' 
the else : 
    Sex = ' M ' 
Print (Sex)
 # above code is equivalent to the following code 

Sex = ' M '  if int (id_card [-2])% 2 == 0 the else  ' M ' 
# # look if, if if satisfied, if compared preceding value, or if the value taken back 
Print (Sex)