Introduction to basic loops in Python

Loop is used to repeatedly execute some program blocks. From the selection structure in the previous lecture, we have seen how to use indentation to indicate the affiliation of program blocks. Similar writing methods are also used for loops.

for loop

The for loop needs to preset the number of loops (n), and then execute the statement belonging to for n times.

The basic structure is

for element in sequence:

statement

For example, we edit a file called forDemo.py

for a in [3,4.4,'life']:
    print a

This loop is to take out an element from the table [3,4.4,'life'] each time (recall: the table is a sequence), then assign this element to a, and then perform the operation belonging to for (print ).

Introducing a new Python function range() to help you create tables.

idx = range(5)
print idx

You can see that idx is [0,1,2,3,4]

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

(About range(), there are many Usage, if you are interested, you can check it out. In Python 3, the usage of range() has changed, see the comment area)

Example

for a in range(10):
    print a**2

while loop

The usage of while is

while condition:

statement

while will continuously loop and execute the statements belonging to it until the condition is False

Example

while i < 10:
    print i
    i = i + 1

Interrupt loop

continue # In a certain execution of the loop, if continue is encountered, then skip this execution and proceed to the next one Operation

break # Stop executing the entire loop

for i in range(10):
    if i == 2: 
        continue
    print i

When the loop is executed to i = 2, the if condition is established, continue is triggered, and this execution is skipped (not execute print) and continue with the next execution (i = 3).

for i in range(10):
    if i == 2:        
        break
    print i

When the loop executes to i = 2, the if condition is established, break is triggered, and the entire loop stops.

Summary

range()

for element in sequence:

while condition:

continue

break

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