3 Looping with for

Looping with for¶

So far, we have covered creating variables of different types and if statements.

Now we want to try looping some code with the keyword for

We will start with a simple example using a List of [3, 5, 7, 9]

In [1]:

for i in [3, 5, 7, 9]:
    print('i is:', i)

for i in [3, 5, 7, 9]: print('i is:', i)

i is: 3
i is: 5
i is: 7
i is: 9

The list could also come from a variable!

In [1]:

aList = [3, 5, 7, 9]

for i in aList:
    print('i is:', i)

aList = [3, 5, 7, 9] for i in aList: print('i is:', i)

i is: 3
i is: 5
i is: 7
i is: 9

When we write

for i in [3, 5, 7, 9]:
    print('i is:', i)

Python will step over the values in the list and assign i to the value at each step.

In the above examples, what is this i? Well it is just a vraiable name we create.

Here is an example where we use something other than i.

In [2]:

aList = [3, 5, 7, 9]

for oneItem in aList:
    print(oneItem)

aList = [3, 5, 7, 9] for oneItem in aList: print(oneItem)

3
5
7
9

Is a string a list?¶

Python is incredibly flexible. For example, a string can be treated like a list.

This makes sense? A string is just a list of characters.

In [3]:

aString = 'abcdefg'

for oneCharacter in aString:
    print(oneCharacter)

aString = 'abcdefg' for oneCharacter in aString: print(oneCharacter)

a
b
c
d
e
f
g

In [4]:

# We can also access a string using our list index with []
aString = 'abcdefg'

print(aString[2])

# We can also access a string using our list index with [] aString = 'abcdefg' print(aString[2])

c

Built in functions like range()¶

We have been using some built in function in Python. Things like if ... else and print().

For looping there is one very useful built in function named range(int). Range takes an integer value and returns a list from 0 up to value-1.

Here are some examples.

In [7]:

for i in range(5):
    print('i is:', i)

for i in range(5): print('i is:', i)

range(0, 5)
i is: 0
i is: 1
i is: 2
i is: 3
i is: 4

In [5]:

# range can of course take an integer variable that we define
myRange = 3
for i in range(myRange):
    print('i is:', i)

# range can of course take an integer variable that we define myRange = 3 for i in range(myRange): print('i is:', i)

i is: 0
i is: 1
i is: 2

Can range(int) take a float? If your not sure, just test it out!

In [9]:

myFloat = 3.14
for i in range(myFloat):
    print('i is:', i)

myFloat = 3.14 for i in range(myFloat): print('i is:', i)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
/Users/cudmore/Dropbox/teaching-2023/iot-fall-2023/docs/docs/3.looping.ipynb Cell 13 line 2
      <a href='vscode-notebook-cell:/Users/cudmore/Dropbox/teaching-2023/iot-fall-2023/docs/docs/3.looping.ipynb#X16sZmlsZQ%3D%3D?line=0'>1</a> myFloat = 3.14
----> <a href='vscode-notebook-cell:/Users/cudmore/Dropbox/teaching-2023/iot-fall-2023/docs/docs/3.looping.ipynb#X16sZmlsZQ%3D%3D?line=1'>2</a> for i in range(myFloat):
      <a href='vscode-notebook-cell:/Users/cudmore/Dropbox/teaching-2023/iot-fall-2023/docs/docs/3.looping.ipynb#X16sZmlsZQ%3D%3D?line=2'>3</a>     print('i is:', i)

TypeError: 'float' object cannot be interpreted as an integer

Nope, range(int) can not take a float. The error is actually informative, it tells us that range(int) by its definition is expecting an int value variable.

TypeError: 'float' object cannot be interpreted as an integer

Tutorial¶

• Make a list of 5 float numbers.
• Write a for loop to print out each items value.

In [6]:

# add you code here (press run in the top toolbar to run your code)

# add you code here (press run in the top toolbar to run your code)