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Python Basic 2 - DataDictionaries: key-value pairs (3/5)
Chapter 3
Python Basic 2 - Data

Dictionaries: key-value pairs

6 minutes read

Beginner friendly

Includes practice

Ever used a real-world dictionary or a phone contact list?
You look up a word (or a name) and instantly get its meaning (or number).
Python’s dictionary works the same way: one side is the key, the other the value.

Runtic's Learning Tips

  • Struggling at first is normal! Every programmer once typed KeyError for the first time.

  • Focus on why a step works, not just what to type; your brain forms stronger links that way.

  • Small daily practice beats a weekend marathon. Ten minutes of “dict” tinkering today builds tomorrow’s confidence.

What is a Dictionary?

A dictionary (dict) is an unordered collection that stores data as pairs:

key ➔ value

Example (a tiny fruit shop stock):

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  • Keys must be unique and immutable (strings, numbers, tuples).
  • Values can be anything (numbers, lists, even other dictionaries).

Creating Your First Dictionary

Inline (literal) method:

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Or start empty then add:

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Try it yourself below.

Practice Challenge

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📝 Your Task:

Create a dictionary named book_priceswith three titles as keys and their prices as values. Then, store the number of items in the dictionary inside len_resultusing the len()function, and print it to confirm.

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Create a dictionary with exactly three key–value pairs, then use len(...) to get its size.

Accessing Values by Key

Get a value using square brackets:

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Safer: dict.get(key, default) avoids crashes if the key is missing.

Adding or Updating Entries

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Removing Entries

del stock["orange"] removes that pair.

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stock.pop("apple", 0) removes and returns the value (0 is fallback).

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Does This Key Exist?

"pear" in stock ➔ True or False

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Useful to prevent errors before accessing.

Looping Through a Dictionary

To go through every key–value pair in a dictionary, use a for loop with two variables: one for the key and one for the value.
This lets you access both parts of each entry inside the loop.

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  • .keys() – iterate keys only.
  • .values() – iterate values only.
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Quick Check-in

Quick Practice

3 minutes

Choose the best answer for each mini-quiz!

Which statement is correct?

`stock.get('mango', 0)` returns ___ if 'mango' is not present.

How would you remove key 'Alice' from dict `grades`?

Practice: Retrieve a Value

Practice Challenge

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📝 Your Task:

Use the given dictionary stockto get the number of bananas and store it in banana_qty.Then, print the result to verify.

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Access the value of "banana" using square brackets or .get().

Quick Summary

  • Dictionaries map unique, immutable keys to values of any type.

  • Common actions: create, access, add/update, delete, test membership, iterate.

  • .get() and the in keyword keep your code safe from missing-key errors.

Lesson Complete!
100%
Progress
What You've Learned:
  • You built, queried, and modified Python dictionaries with confidence.
  • You practiced safe key access and removal to avoid runtime errors.
  • You linked everyday analogies (phonebook) to solid code understanding.

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