Dictionary Methods
clear()
Description: Removes all items from the dictionary.
Example:
my_dict.clear()
print(my_dict) # Outputs {}
copy()
Description: Returns a shallow copy of the dictionary.
Example:
dict_copy = my_dict.copy()
print(dict_copy) # Outputs {'name': 'Alice', 'age': 30, 'city': 'Paris'}
fromkeys(seq, value)
Description: Creates a new dictionary with keys from seq and the value value for each key.
Example:
keys = ['a', 'b', 'c']
default_value = 0
new_dict = dict.fromkeys(keys, default_value)
print(new_dict) # Outputs {'a': 0, 'b': 0, 'c': 0}
get(key, default)
Description: Returns the value for key if key is in the dictionary. If not, returns default.
Example:
value = my_dict.get('name')
print(value) # Outputs 'Alice'
unknown_value = my_dict.get('unknown', 'Not defined')
print(unknown_value) # Outputs 'Not defined'
items()
Description: Returns a view of the dictionary’s key-value pairs.
Example:
pairs = my_dict.items()
print(pairs) # Outputs dict_items([('name', 'Alice'), ('age', 30), ('city', 'Paris')])
keys()
Description: Returns a view of the dictionary’s keys.
Example:
keys = my_dict.keys() print(keys) # Outputs dict_keys(['name', 'age', 'city'])
pop(key, default)
Description: Removes the item with key and returns its value. If key is not found, returns default.
Example:
value_removed = my_dict.pop('age')
print(value_removed) # Outputs 30
print(my_dict) # Outputs {'name': 'Alice', 'city': 'Paris'}
# With default value
missing_value = my_dict.pop('unknown', 'Not found')
print(missing_value) # Outputs 'Not found'
popitem()
Description: Removes and returns a key-value pair from the dictionary. In Python 3.7+, it removes the most recently added pair.
Example:
item = my_dict.popitem()
print(item) # Outputs ('city', 'Paris')
print(my_dict) # Outputs {'name': 'Alice'}
setdefault(key, default)
Description: Returns the value for key if key is in the dictionary. If not, inserts key with the default value and returns default.
Example:
value = my_dict.setdefault('country', 'France')
print(value) # Outputs 'France'
print(my_dict) # Outputs {'name': 'Alice', 'country': 'France'}
update([other])
Description: Updates the dictionary with key-value pairs from another dictionary or iterable of key-value pairs.
Example:
new_elements = {'age': 31, 'profession': 'Engineer'}
my_dict.update(new_elements)
print(my_dict) # Outputs {'name': 'Alice', 'country': 'France', 'age': 31, 'profession': 'Engineer'}
values()
Description: Returns a view of the dictionary’s values.
Example:
values = my_dict.values() print(values) # Outputs dict_values(['Alice', 'France', 31, 'Engineer'])
Dictionary Manipulation
Here are some common manipulations you might find useful:
Adding or Modifying an Element
my_dict['email'] = 'alice@example.com' # Adding
my_dict['age'] = 31 # Modifying
print(my_dict) # Outputs {'name': 'Alice', 'country': 'France', 'age': 31, 'profession': 'Engineer', 'email': 'alice@example.com'}
Removing an Element
del my_dict['email']
print(my_dict) # Outputs {'name': 'Alice', 'country': 'France', 'age': 31, 'profession': 'Engineer'}
Practical Examples
Counting Character Occurrences
text = "hello"
counter = {}
for char in text:
counter[char] = counter.get(char, 0) + 1
print(counter) # Outputs {'h': 1, 'e': 1, 'l': 2, 'o': 1}
Merging Two Dictionaries
dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}
dict1.update(dict2)
print(dict1) # Outputs {'a': 1, 'b': 3, 'c': 4}
Conclusion
Dictionaries in Python are extremely versatile, and their methods allow for effective data manipulation. I hope this lesson has provided a good understanding of the available methods and how to use them. Feel free to experiment and explore further to fully master dictionaries in Python.