Python loops

Repeat one or more statements

---

Python loops repeat code, there are two common loops which are for and while loops which we go over in this article.

Loops are a way to do iteration, to repeat code. In general developers follow the priniciple of dont repeat yourself (dry). This means they would rather use a loop than type the same lines of code 1000 times.

Related course: Complete Python Programming Course & Exercises

While loops

While loops look like this:

n = 6
while n > 0:
    print(n)
    print('check it')
    n = n - 1
print('Loop out')
print(n)

The outputs are.

6  
Check it.  
5  
Check it.  
4  
Check it.  
3  
Check it.  
2  
Check it.  
1  
Check it.  
Loop out  
0

_ Fact 2: _ Loop-break
For example.

while True:
    line = input('>>')
    if line == 'done':
        break
    print(line)
print('Done!')

The output is.

> > asdaa  
> > asdaa
> 
> > sdfsd  
> > sdfsd
> 
> > done  
> > Done!

* * * *

Note: BREAK is jumping out of the current loop! Move to the last line of the module. (Jumping down), in contrast to CONTINUE.

_ Fact 3: _ Jump to the top of the current loop, continue

while True:
    line = input('>>')
    if line[0] == '#':
        continue
    elif line == 'done':
        break
    print(line)
print('Done!')

The output is.

> > qwe  
> > qwe
> 
> > > #Hello  
> > Hello  
> > Hello
> 
> > done  
> > Done!

But the prerequisite is that there is no other loop under that loop, because it essentially jumps out of the current loop and onto the next one.

For loop

_Fact 4: _ Definite loop, which is the for loop

friends = ['Gary' , 'Tom' , 'Curry']
for friend in friends:
    print(friend)
print('Done!')

The output is.

Gary.  
Tom.  
Curry.  
Done!  
for is mainly used for strings, arrays, etc.

_Fact 5: _ The usefulness of the several for's given, such as counting numbers, summing, averaging, filtering out the numbers that fit the requi

_ Fact 6: _ introduces another type of variable, Boolean type, only True and False

_ Fact 7: _ introduces another type of variable, which is None, for example.

smallest = None # is equivalent to a flag value
for value in [2,5,35,23,678,54,12 , 0 , -3]:
    if smallest is None: #judgment is the first time into for loop, which can be understood as start, trigger.
        smallest = value
    elif value < smallest:
        smallest = value
print(smallest)
print('Done')

• Usually the comparative size is assigned a value to the smallest at the first, but this value is not universal, so use None
• Note that the IS, here, is very similar to the "==", but much stronger
• Similarly, there is also is not
• the double equivalence sign is a common mathematical thing. **