# basic flow control in python

2020-06-08

|

|

371 words

Continuing my basics education of Python, here are some examples of flow control.

I’ll explore the following:

1. If, else if, and else
2. Iterating over lists
3. Break statements
4. Ranges, starts, ends and steps
5. While loops

## If, Else If, and Else

if_elif_else.py
``````# if, elif, else
x = int(input("enter an integer: "))
if x < 0:
x = 0
print('Negative number set to 0.')
elif x == 0:
print('zero')
elif x == 1:
print('one')
else:
print('some other number')``````

## Iterating Over Lists

lists.py
``````pets = ['Cat', 'Dog', 'Elephant', 'Hamster']

for pet in pets:
print(f'I have a {pet}.')``````

When we run this, python will iterate over the list:

``````\$ python lists.py
I have a Cat.
I have a Dog.
I have a Elephant.
I have a Hamster.``````

In the next example, we’ll break out of the iteration if we see a Dog:

no_dogs.py
``````pets = ['Cat', 'Dog', 'Elephant', 'Hamster']

for pet in pets:
if pet == 'Dog':
print('No dogs allowed!')
break
else:
print(f"We love {pet}s!")``````

For example:

``````\$ python no_dogs.py
We love Cats!
No dogs allowed!``````

## Ranges

When using ranges, there are up to three parameters and behavior changes depending on how many are provided. In all cases, the range is inclusive of the start and non-inclusive of the end.

ranges.py
``````for i in range(5):
print(i)

for i in range(10, 15):
#          (start, end)
print(i)

for i in range(0, 30, 5):
#         (start, end, step)
print(i)

for i in range(30, 0, -5):
print(i)``````

With just one argument, the value is the end of the range. With two, we have a start and end. WIth three we have start, end, and step/increment. The increment can be positive or negative.

## While Loops

The while loop will continue to operate as long as it remains true.

while.py
``````# while loops
x = 0
while x < 10:
print(x)
x += 1``````

In this case, the while loop evaluates if x is less than 10. While true, it prints x and then increments x.

Related Posts
• Exploring Python Methods With Help And Dir

• Hi there and thanks for reading! My name's Stephen. I live in Chicago with my wife, Kate, and dog, Finn. Want more? See about and get in touch!