Condition and loop

Condition and loop
1. if statement

 

 1 >>>a=7 2 >>> if a<0: 3 ...     print 'Negative changed to zero' 4 ... elif a==0: 5 ...     print 'Zero' 6 ... elif a==1: 7 ...     print 'Single' 8 ... else: 9 ...     print 'More'10 ...     11 More

 

Elif is short for 'else if'. The use of the if statement implements switch case statement usage.

2. for statement

 

1 >>> words = ['cat','fish','window']2 >>> for w in words[:]:3 ...     if len(w)>5:4 ...         words.insert(0,w)5 ...         6 >>> words7 ['window', 'cat', 'fish', 'window']

 

Note: words [:]. If it is words, it becomes an endless loop. If you modify the list in the traversal list loop, we recommend that you copy the list first.

 

 

3. range () function

 

This function is used to create a new table. The elements in this table are all integers. Starting from 0, the next element is 1 larger than the previous one until the upper limit written in the function (excluding the upper limit itself ).

 1 >>> range(10) 2 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 3 >>> range(0,10,3) 4 [0, 3, 6, 9] 5  6 >>> a=['Mary','had','a','little','lamb'] 7 >>> for i in range(len(a)): 8 ...     print i,a[i] 9 ...     10 0 Mary11 1 had12 2 a13 3 little14 4 lamb

4. break and continue statements

 

Continue # If a continue is encountered during a loop execution, skip this execution and perform the next operation.

 

Break # Stop the entire execution cycle

1 >>> for i in range(5):2 ...     if i==2:3 ...         continue4 ...     print i5 ...     6 07 18 39 4

When the loop is executed to I = 2, The if condition is true, and the continue is triggered. Skip this execution (do not execute print) and continue the next execution (I = 3 ).

>>> for i in range(5):...     if i==2:...         break...     print i...     01

When the loop is executed to I = 2, The if condition is true, the break is triggered, and the entire loop is stopped.

5. Summary

Range ()

For element in sequence:

While condition:

Continue

Break