Learn Python
- Python basic
- Introduction to File Handling
- Basics of List Comprehension
- Introduction to Matplotlib
- Classes and Objects
- Introduction to Functions
- Python Numbers
- Creating Basic Plots
- Opening and closing files
- Function parameters and arguments
- Advanced Techniques
- Attributes and Methods
- Python Strings
- Scope and lifetime of variables
- Advanced Plotting
- Reading from files
- Performance and Limitations
- Encapsulation
- Python List
- Specialized Plots
- Writing to files
- Return statement and output
- Inheritance
- Python Tuple
- Advanced Customization
- Working with different file formats
- Lambda Functions
- Polymorphism
- Practical Applications
- Special Methods
Python Dictionaries
Common dictionary methods
These are common dictionary methods:
- get(key, default=None)
This method is used to retrieve the value associated with a specific key in a dictionary. It takes two arguments:
- key: The key you want to access the value for.
- default (optional): A default value to return if the key doesn't exist in the dictionary. This argument defaults to None if not provided.
Example:
my_dict = {"name": "David", "age": 35}
value = my_dict.get("name") # Returns "David" (key exists)
missing_value = my_dict.get("city", "Unknown") # Returns "Unknown" (key doesn't exist)- keys()
This method returns a view object containing all the keys present in the dictionary. This view object is dynamic, meaning any changes made to the dictionary itself will be reflected in the view. However, you cannot directly modify the dictionary through the view.
Example:
my_dict = {"name": "Emily", "age": 28, "city": "Seattle"}
keys_view = my_dict.keys() # keys_view is a view object
# Print all keys (using a loop)
for key in keys_view:
print(key) # Output: name, age, city- values()
This method returns a view object containing all the values present in the dictionary. Similar to keys(), it's a dynamic view, reflecting changes in the dictionary.
Example:
my_dict = {"name": "Frank", "age": 42, "occupation": "Teacher"}
values_view = my_dict.values() # values_view is a view object
# Print all values (using a loop)
for value in values_view:
print(value) # Output: Frank, 42, Teacher- items()
This method returns a view object containing all the key-value pairs in the dictionary as tuples.
Each tuple in the view represents a single key-value pair.
Example:
my_dict = {"name": "Grace", "age": 30, "city": "Chicago"}
items_view = my_dict.items() # items_view is a view object
# Print all key-value pairs (using a loop)
for key, value in items_view:
print(f"{key}: {value}") # Output: name: Grace, age: 30, city: Chicago- pop(key, default=None)
This method removes the key-value pair associated with a specific key from the dictionary and returns the value. It takes two arguments:
- key: The key of the pair you want to remove.
- default (optional): A default value to return if the key doesn't exist. This argument defaults to None if not provided.
Important: Using pop without the default argument and trying to remove a non-existent key will raise a KeyError.
Example:
my_dict = {"name": "Henry", "age": 50}
removed_value = my_dict.pop("age") # Returns 50 and removes the "age" key-value pair
# Trying to pop a non-existent key without default will raise a KeyError
# missing_value = my_dict.pop("city") # Raises KeyError
safe_removal = my_dict.pop("city", "N/A") # Returns "N/A" (key doesn't exist)- popitem()
This method removes and returns an arbitrary key-value pair from the dictionary.
You cannot specify which key-value pair to remove; it's chosen from the dictionary internally.
Example:
my_dict = {"name": "Isla", "age": 22, "country": "Canada"}
removed_pair = my_dict.popitem() # Returns a tuple containing a key-value pair (e.g., ("country", "Canada"))It's time to take a quiz!
Test your knowledge and see what you've just learned.
What does the get() method return if the specified key does not exist?
ARaises a KeyError
BReturns a default value
CReturns None
DReturns an empty string
Check Answer
What does the keys() method return?
AA view object of all keys in the dictionary
BA list of all values in the dictionary
CA tuple of all key-value pairs
DA copy of the dictionary
Check Answer
What does the values() method return?
AA list of all keys in the dictionary
BA view object of all key-value pairs
CA view object of all values in the dictionary
DA copy of the dictionary
Check Answer
What does the items() method return?
AA view object of all keys
BA view object of all key-value pairs as tuples
CA view object of all values
DA copy of the dictionary
Check Answer
What happens if you use pop() on a non-existent key without a default value?
ARaises a KeyError
BReturns None
CReturns a default value
DReturns an empty string
Check Answer
What does the popitem() method do?
DRemoves and returns all key-value pairs
ARemoves and returns a specified key-value pair
BRemoves and returns an arbitrary key-value pair
CReturns the last key-value pair without removing it
Check Answer