Python challenge: Handling lists

Here are some very simple operations that can be performed on lists:

Initialize an empty list

names = []

Adding a string to the list

names.append("Martin")

Inserting a new string at a custom position

names.insert(0, "Kalle")

Deleting an item from the list

One way of deleting an item is the del function:

del names[0]

Another alernative is the remove function:

names.remove("test")

Note that this call can cause a ValueError, if the list does not contain such an object.

Checking if the list contains a certain string

if names.count("Joe") > 0:
  ...

The function count returns a value larger than 0, if the list contains the string in question.

Sorting the list

names.sort()

Getting the size of the list

len(names)

Lists that contain complex objects

Of course, lists can also contain non-primitive objects. The following code iterates through a list of objects of type Contact and calls the displayContact function.

for contact in contacts:
  contact.displayContact()

Sorting the list based on a certain criteria

Lists that contain complex atttributes can be sorted based on such an attribute.

new_list = sorted(contacts, key=lambda x: x.firstname, reverse=False)

This will sort the contact list ascending based on their firstname. The sorted function returns a new, sorted list and keep the original list unchanged. The content of the new list is as follows:

Sorting the list based on the first name 
Bob, Marley, mail, 071666224
Jane, Doe, mail, 01356867566
Laurel, Aitken, mail, 983444566
Martin, Bäumer, mail, 0786777566

Using list comprehension

Above, I have used a standard for loop to iterate through a list. This can be replaced by a list comprehension:

[contact.displayContact() for contact in contacts]

A comprehension contains an expression followed by a for statement. The idea of comprehensions is to shorten the code and to make it easier to read.

Filtering a list using list comprehension

Comprehensions can be also used to filter lists, that is we can search through a list for matching items. The following example finds all contacts that have phone numbers containing the number 1:

[contact.displayContact() for contact in contacts if "1" in contact.phone]

Further resources

A working example can be found on github