Skip to main content

Dictionaries in Python

 

Learning Sections      show

Dictionaries in Python

A dictionary in Python is a collection of key-value pairs. Here are some common methods used with dictionaries:

1. clear()

Removes all items from the dictionary.


# Clear the dictionary
my_dict.clear()
print(my_dict)  # Output: {}

2. copy()

Returns a shallow copy of the dictionary.


# Create a shallow copy of the dictionary
new_dict = my_dict.copy()

3. fromkeys()

Returns a new dictionary with the specified keys and the same value for each key.


# Create a dictionary with specified keys and default value
keys = ['a', 'b', 'c']
default_value = 'default'
new_dict = dict.fromkeys(keys, default_value)
print(new_dict)  # Output: {'a': 'default', 'b': 'default', 'c': 'default'}

4. get()

Returns the value for the specified key. Returns None if the key is not found.


# Get the value for a key
value = my_dict.get('key')
print(value)  # Output: None (if 'key' is not found)

5. items()

Returns a view object that displays a list of key-value tuple pairs.


# Get a view object of key-value pairs
items = my_dict.items()
print(items)  # Output: dict_items([('key1', 'value1'), ('key2', 'value2'), ...])

6. keys()

Returns a view object that displays a list of all the keys in the dictionary.


# Get a view object of keys
keys = my_dict.keys()
print(keys)  # Output: dict_keys(['key1', 'key2', ...])

7. pop()

Removes the element with the specified key and returns its value. Raises a KeyError if the key is not found.


# Remove and return the value for a key
value = my_dict.pop('key')
print(value)  # Output: 'value' (if 'key' is found)

8. popitem()

Removes and returns an arbitrary key-value pair as a tuple. Raises a KeyError if the dictionary is empty.


# Remove and return an arbitrary key-value pair
key, value = my_dict.popitem()
print(key, value)  # Output: ('key', 'value')

9. setdefault()

Returns the value of the specified key. If the key does not exist, inserts the key with the specified value.


# Get the value for a key; if key does not exist, insert key with specified value
value = my_dict.setdefault('key', 'default_value')
print(value)  # Output: 'value' (if 'key' exists), 'default_value' (if 'key' does not exist)

10. update()

Updates the dictionary with the specified key-value pairs.


# Update the dictionary with key-value pairs from another dictionary
other_dict = {'key1': 'new_value1', 'key2': 'new_value2'}
my_dict.update(other_dict)
print(my_dict)

11. values()

Returns a view object that displays a list of all the values in the dictionary.


# Get a view object of values
values = my_dict.values()
print(values)  # Output: dict_values(['value1', 'value2
'])
Labels:

Popular posts from this blog

Generators in Python

  Learning Sections          show Generators in Python Generators are a special type of iterator in Python that allow you to iterate over a sequence of items without storing them all in memory at once. They are useful for generating large sequences of data on-the-fly, or for processing data in a memory-efficient manner. Creating Generators In Python, generators are created using generator functions or generator expressions: # Generator function def my_generator ( n ): for i in range ( n ): yield i # Generator expression my_generator = ( i for i in range ( 10 )) A generator function uses the yield keyword to yield values one at a time, while a generator expression creates an anonymous generator. Iterating Over Generators You can iterate over the values produced by a generator using a for loop: for value in my_generator ( 5 ): print ( value ) This w...
Read more

Walrus Operator in Python

  Learning Sections          show Walrus Operator in Python The walrus operator ( := ) is a new assignment operator introduced in Python 3.8. It allows you to assign values to variables as part of an expression, making certain constructs more concise. Basic Usage The basic syntax for the walrus operator is: variable_name := expression Here, variable_name is assigned the value of expression , and the result of the expression is also returned. Example: Simplifying Code Consider the following example where we find and print the length of a list if it's greater than 3: # Without walrus operator my_list = [ 1 , 2 , 3 , 4 ] if len ( my_list ) > 3 : length = len ( my_list ) print ( length ) # With walrus operator my_list = [ 1 , 2 , 3 , 4 ] if ( length := len ( my_list )) > 3 : print ( length ) In the second example, the walrus operator assigns the result of len(my...
Read more

Lambda Functions in Python

  Learning Sections          show Lambda Functions in Python Lambda functions, also known as anonymous functions, are small, unnamed functions defined with the lambda keyword. They can have any number of arguments but only one expression. Lambda functions are often used for short, throwaway functions that are not needed elsewhere in the code. 1. Basic Syntax The syntax for a lambda function is: lambda arguments : expression Example: add = lambda x , y : x + y print ( add ( 2 , 3 )) # Output: 5 2. Using Lambda with Built-in Functions Lambda functions are commonly used with built-in functions like map() , filter() , and sorted() . Example with map() : numbers = [ 1 , 2 , 3 , 4 , 5 ] squared = map ( lambda x : x ** 2 , numbers ) print ( list ( squared )) # Output: [1, 4, 9, 16, 25] Example with filter() : numbers = [ 1 , 2 , 3 , 4 , 5 ] even = filter ( lambd...
Read more