Python fourth day learning the basics

Statements and expressions

Code format: PEP8 indented four spaces no more than 79 characters in a row

A statement

1, assignment statement: example: s = 'Python'

2, tuple / list assignment

3, sequence assignment

Sequence assignment, when the variable does not match with the character of error. This time we need to use greedy matching [* b] preceded by a star.

Second, the expression

1, the function call statement:

For example, there is a square root function math module. After importing the call is called a function call

2, the method call

3, literals

4、print（‘hello’）

if conditional statement

Block of code is determined by one or more of the execution result of the statement (True or False).

= the INPUT name ( ' Please enter your user name: ' ) 

IF name == " ADMIN " :
     Print ( " super administrator " )
 elif name == " the User " :
     Print ( " average user " )
 elif name == " the Guest " :
     Print ( " guest " )
 the else :
     Print ( " do not know you ." )

　　Behind each condition where a colon (:), indicating that the following condition is satisfied after the statement block to be executed.

　　Use indentation divided statement blocks, the number of statements in the same indentation together to form a block.

　　No switch in Python - case statement.

if the operator common operation

Operators	description
`<`	Smaller than
`<=`	less than or equal to
`>`	more than the
`>=`	greater than or equal to
`==`	Equal, compare objects for equality
`!=`	not equal to

if nested

In the nested if statements, can if ... elif ... else in another configuration if ... elif ... else structure.

if expression 1:

    Statement 
    if expression 2: 
        Statement 
    elif expression 3: 
        Statement 
    else 
        Statement 
elif expression 4: 
    Statement 
else: 
    statement

while loop

We meet the conditions (conditional statement returns True) then loop a section of code execution

= 0 COUNT 
the while COUNT <5: 
   Print (COUNT, "less than 5") 
   COUNT = COUNT +. 1 
the else: 
   Print (COUNT, "greater than or equal to 5")

for loop

Frequently used in a sequence of objects (such as lists, tuples etc.) to traverse

The general format for the following cycle:

for i in range(5):
    print(i)

break, continue and cyclic else Clauses

break statement can jump out of the loop for a while and. If you break out or for while loop, any corresponding loop else block will not be executed

for letter in 'Runoob': # first instance 
   IF Letter == 'B': 
      BREAK 
   Print ( 'current letters:', Letter) 
  
var # 10 = second instance of 
the while var> 0:               
   Print ( 'profit variable value: ', var) 
   var var = -1 
   IF == var. 5: 
      BREAK 

Print () "Good BYE!"

continue statement is used to tell Python skip the remaining statements in the current loop block, and then proceed with the next cycle.

for letter in 'Runoob': # first instance 
   if letter == 'o': # o is the output alphabet skipped 
      Continue 
   Print ( 'the current letter:', Letter) 

var # 10 = second instance 
while var> 0:               
   var var = -1 
   IF == var. 5: 5 # skip variable output 
      Continue 
   Print ( 'the current variable values:', var) 
( "! Good BYE") Print

Loop else clause can have it in an exhaustive list (with a for loop) or the condition becomes false (with while loop) cause to be executed when the loop terminates, but does not perform the loop is terminated break.

for n- in Range (2, 10 ):
     for X in Range (2 , n-):
         IF n-% X == 0:
             Print (n-, ' equal ' , X, ' * ' , // n- X)
             BREAK 
    the else :
         # loop elements not found 
        Print (n-, ' is a prime ' )

Note:

breakStatement to exit the loop cycle, and continuestatements can be ended prematurely round cycle, and directly start the next cycle. These two statements are usually must cooperate ifstatements.

Sometimes there are problems if the code is written, make the program into a "death cycle", that is, loop forever. Available Ctrl+Cexit the program, or to force the end of the Python process.

Python fourth day learning the basics

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