Python: LISTS AND FUNCTIONS by Tushar Gahora

LISTS AND FUNCTIONS

Appending to a list

Here, we’ll quickly recap how to .append() elements to the end of a list.

i.e

 n= [11, 16]

# Append the number 27 here

n.append(27)

print(n)

Removing elements from lists

This exercise will expand on ways to remove items from a list. You actually have a few options. For a list called n:

1. n.pop(index) will remove the item at index from the list and return it to you:

   
   n = [9, 5, 8, 7]
   n.pop(1)
   # Returns 5 (the item at index 1)
   print n
   # prints [9, 8, 7]
   

2. n.remove(item) will remove the actual item if it finds it:

   
   n.remove(1)
   # Removes 1 from the list,
   # NOT the item at index 1
   print n
   # prints [9, 8, 7]
   

3. del(n[1]) is like .pop in that it will remove the item at the given index, but it won’t return it:

   
   del(n[1])
   # Doesn't return anything
   print n
   # prints [9, 8, 7]
   

4.  

Printing out a list item by item in a function

This exercise will go over how to utilize every element in a list in a function. You can use the existing code to complete the exercise and see how running this operation inside a function isn’t much different from running this operation outside a function.

Don’t worry about the range function quite yet—we’ll explain it later in this section.

Passing a range into a function

Okay! Range time. The Python range() function is just a shortcut for generating a list, so you can use ranges in all the same places you can use lists.

range(6) # => [0, 1, 2, 3, 4, 5]
range(1, 6) # => [1, 2, 3, 4, 5]
range(1, 6, 3) # => [1, 4]

The range function has three different versions:

1. range(stop)
2. range(start, stop)
3. range(start, stop, step)

In all cases, the range() the function returns a list of numbers from start up to (but not including) stop. Each item increases by step.

If omitted, start defaults to 0 and step defaults to 1.

Iterating over a list in a function

Now that we’ve learned about range, we have two ways of iterating through a list.

Method 1 - for item in list:

for item in list:
  print item

Method 2 - iterate through indexes:

for i in range(len(list)):
  print list[i]

Method 1 is useful to loop through the list, but it’s not possible to modify the list this way.

Method 2 uses indexes to loop through the list, making it possible to also modify the list if needed. Since we aren’t modifying the list, feel free to use either one on this lesson!

Using strings in lists in functions

Now let’s try working with strings!

for item in list:
  print item

for i in range(len(list)):
  print list[i]

The example above is just a reminder of the two methods for iterating over a list.

Using two lists as two arguments in a function

Using multiple lists in a function is no different from just using multiple arguments in a function!

a = [11, 16, 27]
b = [1, 5, 10]
print a + b
# prints [11, 16, 27, 1, 5, 10]

The example above is just a reminder of how to concatenate two lists.

Using a list of lists in a function

Finally, this exercise shows how to make use of a single list that contains multiple lists and how to use them in a function.

list_of_lists = [[1, 2, 3], [4, 5, 6]]

for lst in list_of_lists:
  for item in lst:
    print item

1. In the example above, we first create a list containing two items, each of which is a list of numbers.
2. Then, we iterate through our outer list.
3. For each of the two inner lists (as lst), we iterate through the numbers (as item) and print them out.

We end up printing out:

1
2
3
4
5
6