Chapter 9 - Dictionaries in Python

Chapter 9 of the Python textbook, Python for Everybody: Exploring Data Using Python 3 by Dr Charles R. Severance, covers dictionaries, which are fundamental data structures in Python. Here are the significant points of each section along with explanations and examples:

Section 9.1: Dictionaries

• Dictionaries are similar to lists but more general; they map keys to values.
• Keys can be almost any data type.
• You can create an empty dictionary using {}.
• To add items to a dictionary, use square brackets.

Example:

eng2sp = dict()

eng2sp['one'] = 'uno'

Section 9.2: Dictionary as a Set of Counters

• Dictionaries can be used to count the occurrence of items.
• You can create a dictionary to count characters in a string or words in a text.

Example:

word = 'brontosaurus'

counts = dict()

for c in word:

    if c not in counts:

        counts[c] = 1

    else:

        counts[c] += 1

Section 9.3: Looping and Dictionaries

• for loop can be used to iterate over keys in a dictionary.
• You can iterate over keys, values, or both in a dictionary using dictionary methods.
• The get() method simplifies dictionary value retrieval and is a common idiom.

Example:

counts = { 'chuck': 1, 'annie': 42, 'jan': 100}

for key in counts:

    print(key, counts[key])

Section 9.4: Advanced Text Parsing

• Dictionaries can be used to parse text and count occurrences of words.
• You can use string methods to preprocess text, like removing punctuation and converting to lowercase.
• Python's string.punctuation provides a set of punctuation characters.

Example:

import string

line = "But, soft! what light through yonder window breaks?"

line = line.translate(line.maketrans('', '', string.punctuation))

line = line.lower()

words = line.split()

Section 9.5: Debugging

• Debugging becomes essential as data sets get larger.
• Strategies for debugging include scaling down input, checking summaries and types, writing self-checks, and pretty-printing output.

This chapter introduces dictionaries as a powerful data structure for various tasks, including counting and mapping items. Understanding dictionaries and their usage is crucial for many real-world programming scenarios.

Key Terms:

• Dictionary
• Hashtable
• Hash Function
• Histogram
• Implementation
• Item
• Key-Value Pair
• Lookup
• Nested Loops
• Value

Conclusion

This chapter introduces dictionaries as a powerful data structure for various tasks, including counting and mapping items.

Understanding dictionaries and their usage is crucial for many real-world programming scenarios.

Complete exercise 9 before proceeding to read chapter 10

 

Chapter 9 of the Book: Python for Everybody: Exploring Data Using Python 3 by Dr. Charles R. Severance (Available in pdf: http://do1.dr-chuck.com/pythonlearn/EN_us/pythonlearn.pdf).