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Questions and Answers
What is a collection?
What is a collection?
A collection is a data structure that allows storing more than one value in a single variable.
What is a dictionary in Python?
What is a dictionary in Python?
A dictionary is a data structure that stores values with unique labels (keys) allowing for fast lookups.
In Python, a list indexes its entries based on the position in the list.
In Python, a list indexes its entries based on the position in the list.
True
Dictionaries maintain the order of their entries like lists.
Dictionaries maintain the order of their entries like lists.
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Which of the following is NOT a common name for a dictionary in another programming language?
Which of the following is NOT a common name for a dictionary in another programming language?
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What is a Dictionary Literal?
What is a Dictionary Literal?
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The command to create an empty dictionary is _____.
The command to create an empty dictionary is _____.
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What happens if you try to reference a key that is not in a dictionary?
What happens if you try to reference a key that is not in a dictionary?
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How can you count occurrences of items using dictionaries?
How can you count occurrences of items using dictionaries?
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Study Notes
Overview of Collections
- A collection allows multiple values to be stored within a single variable.
- Collections enable convenient management of multiple data points.
Difference between Collections and Single Values
- Standard variables typically hold a single value; assigning a new value overwrites the old one.
Types of Collections
- List: A linear, ordered collection of values.
- Dictionary: A collection of key-value pairs, often referred to as a "bag" of values with unique labels.
Python Dictionaries
- Dictionaries are Python's powerful data collection feature, enabling quick database-like operations.
- Known as associative arrays in Perl/PHP, properties or Maps in Java, and Property Bags in C#/.Net.
Dictionary Operations
- Values in dictionaries are indexed by keys, not by position like in lists.
- Example of creating a dictionary:
-
purse = dict() - Adding items:
purse['money'] = 12 - Accessing values:
print(purse['candy'])returns the value associated with the 'candy' key.
-
Comparing Lists and Dictionaries
- Lists use numerical indices to access items, while dictionaries use keys for lookups.
- Example comparison highlights:
- List:
lst = [21, 183] - Dictionary:
ddd = {'age': 21, 'course': 182}
- List:
Dictionary Literals
- Defined using curly braces with key:value pairs.
- Can create an empty dictionary using
{}.
Practical Use of Dictionaries
- Common applications include counting occurrences of data.
- Example:
- Initiating a counter:
ccc = dict() - Incrementing counts:
ccc['cwen'] = ccc['cwen'] + 1.
- Initiating a counter:
Error Handling in Dictionaries
- Attempting to access a key that doesn't exist raises a KeyError.
- Use the
inoperator to check for key existence before attempting access.
Adding New Entries
- When encountering a new key, it’s added to the dictionary to keep track of frequency or occurrence.
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Description
Explore the concept of collections in Python, particularly focusing on dictionaries. This quiz covers what constitutes a collection and compares it to standard variables, providing insights into their utility and functionality. Test your understanding of how multiple values can be stored and accessed in Python dictionaries.
