Defaultdicts

"""
"""

from collections import defaultdict

# Creating a defaultdict with int
int_dict = defaultdict(int)

# Adding elements
int_dict['a'] += 1    # Increments the value of 'a' by 1
int_dict['b'] += 2    # Increments the value of 'b' by 2

# Creating a defaultdict with list
list_dict = defaultdict(list)

# Adding elements
list_dict['a'].append(1)    # Appends 1 to the list associated with 'a'
list_dict['b'].append(2)    # Appends 2 to the list associated with 'b'

# Creating a defaultdict with a custom default factory
def default_value():
    return 'default'

custom_dict = defaultdict(default_value)

# Accessing elements
print(custom_dict['a'])    # Accessing a non-existent key returns 'default'
custom_dict['b'] = 'value'
print(custom_dict['b'])    # Accessing an existing key returns 'value'

# Iterating through defaultdict
for key, value in int_dict.items():
    print(f"{key}: {value}")  # Prints each key-value pair in int_dict

for key, value in list_dict.items():
    print(f"{key}: {value}")  # Prints each key-value pair in list_dict

# Checking for existence of a key (gotcha)
# Accessing a non-existent key in defaultdict will create the key with the default value
print('c' in int_dict)  # False, 'c' does not exist
_ = int_dict['c']       # Accessing 'c', which creates it with default value 0
print('c' in int_dict)  # True, 'c' now exists

# Example usage
print("int_dict:", int_dict)
print("list_dict:", list_dict)
print("custom_dict:", custom_dict)

# Showing the gotcha
# The gotcha with defaultdict is that accessing a non-existent key creates it with the default value.
another_dict = defaultdict(list)
print("Before accessing a non-existent key:", another_dict)
print(another_dict['new_key'])  # Accessing 'new_key', which creates it with default value (an empty list)
print("After accessing a non-existent key:", another_dict)

# Example demonstrating common use case of defaultdict with lists
word_count = defaultdict(int)
words = "the quick brown fox jumps over the lazy dog".split()
for word in words:
    word_count[word] += 1
print("Word count:", word_count)