Python_ Control Statement 3

1. Conditional Judgment

1.If...else

If judging condition:

EXECUTE statement ...

Else

EXECUTE statement ...

2.If...elif: python does not support switch statements

example:num = 5

if num = = 3: # To determine the value of num

print ' Boss '

elif num = = 2:

print ' user '

elif num = = 1:

print ' worker '

Elif num < 0: # value is less than zero output

print ' ERROR '

Else

print ' Roadman ' # conditions are not set when the output

2. Looping statements

The while loop executes the loop body when the given judgment condition is true, otherwise exits the loop body.

The For Loop repeats the execution of the statement

Nested Loops you can nest A for loop in the while loop body

1.While Loop statement

While judging condition:

EXECUTE statement ...

Example:count = 0

while (Count < 9):

print ' The count is: ', count

Count = Count + 1

Print "Good bye!"

looping with else statements

Example:count = 0

While Count < 5:

Print count, "is less than 5"

Count = Count + 1

Else

Print count, "is isn't less than 5"

While statement when two important commands Continue,break to skip loops, Continue is used to skip the loop

i = 1

While I < 10:

i + = 1

If i%2 > 0: # Skip output when non-even

Continue

Print I # output 2, 4, 6, 8, 10

i = 1

While 1: # The loop condition is 1 must be set

Print I # output 1~10

i + = 1

If i > 10: # When I is greater than 10 o'clock jump out of the loop

Break

2.F or Loop

For...in.

Example:for letter in ' Python ': # First Instance

print ' Current letters: ', letter

looping with else statements

Example:for num in range (10,20): # iterations between 10 and 20 digits

For I in Range (2,num): # based on factor iterations

If num%i = = 0: # Determine the first factor

J=num/i # Calculates a second factor

print '%d equals%d *%d '% (num,i,j)

Break # jumps out of the current loop

Else: # The else part of the loop

Print num, ' is a prime number '

3.Python Loop Nesting

Python for loop nesting syntax:

For Iterating_var in sequence:

For Iterating_var in sequence:

Statements (s)

Statements (s)

Python while loop nesting syntax:

While expression:

While expression:

Statement (s)

Statement (s)

Instance:

The following instance uses the prime number between the nested loop output 2~100:

i = 2

while (I < 100):

j = 2

while (J <= (i/j)):

If not (I%J): Break

j = j + 1

if (J > i/j): Print I, "is prime"

i = i + 1

Print "Good bye!"

5. Circular control Statements

Break statement

The break statement is used to terminate the loop statement, which is used in the while and for loops.

If you use a nested loop,the break statement stops executing the deepest loop and starts executing the next line of code.

Example (Python 2.0+)

#!/usr/bin/python

#-*-Coding:utf-8-*-

For letter in ' Python ': # First Instance

If letter = = ' h ':

Break

print ' Current letters: ', letter

var = 10 # A second instance

While var > 0:

print ' current variable value: ', var

var = var-1

if var = = 5: # when variable var equals 5 o'clock Exit loop

Break

Print "Good bye!"

Continue statements

The Python continue statement jumps out of the loop, and break jumps out of the loop.

The continue statement is used to tell Python to skip the remaining statements of the current loop, and then proceed to the next round of loops.

The continue statement is used in the while and for loops.

Instance:

Example (Python 2.0+)

#!/usr/bin/python

#-*-Coding:utf-8-*-

For letter in ' Python ': # First Instance

If letter = = ' h ':

Continue

print ' Current letters: ', letter

var = 10 # A second instance

While var > 0:

var = var-1

if var = = 5:

Continue

print ' current variable value: ', var

Print "Good bye!"

Pass Statement

The Python Pass is an empty statement in order to maintain the integrity of the program structure.

Pass does not do anything, generally used as a placeholder statement.

Instance:

#!/usr/bin/python

#-*-Coding:utf-8-*-

# output Python for each letter

For letter in ' Python ':

If letter = = ' h ':

Pass

print ' This is a pass block '

print ' Current letters: ', letter

Print "Good bye!"

Python_ Control Statement 3