Python language basics 55: items and values in a dictionary

Introduction

In the previous post we saw how to copy a set. Both the copy function and the set constructor create shallow copies with all its consequences.

In this post we’ll discuss how to retrieve and iterate over the keys and values of a dictionary.

Looping through a dictionary

We’ve already seen how to loop through a dictionary with a for-each loop in this post. Here’s a reminder:

sizes = {"S": "Small", "M": "Medium", "L": "Large", "XL": "X-Large"}

Here’s how we can print the key and value of each element in a for-loop:

for size in sizes:
    print("Key ", size, ", value: ", sizes[size])

…which prints the following:

Key L , value: Large
Key S , value: Small
Key M , value: Medium
Key XL , value: X-Large

However, there are other key and value related functions available for a dictionary.

Keys only

You can get hold of the keys only using the keys function:

for key in sizes.keys():
    print(key)

XL
M
L
S

Note that there’s no predefined sort order for the items in the dictionary. If you test the above code you may very well see a different key order.

Values only

There’s an equivalent function to retrieve the values in the dictionary:

for val in sizes.values():
    print(val)

Medium
Small
Large
X-Large

Values and items

Finally there’s the items function which returns the key-value pairs in a tuple:

for item in sizes.items():
    print(item)

(‘M’, ‘Medium’)
(‘L’, ‘Large’)
(‘S’, ‘Small’)
(‘XL’, ‘X-Large’)

The elements in the tuple can be assigned to comma-delimited variables for convenient access:

for key, value in sizes.items():
    print("Key: {0}, value: {1}".format(key, value))

Key: L, value: Large
Key: S, value: Small
Key: M, value: Medium
Key: XL, value: X-Large

In the next post we’ll see how to update a dictionary.

Read all Python-related posts on this blog here.