Dictionary Python

Iterate over a dictionary in Python

Iterate over a dictionary in Python

Employing the keys() Method

Python dictionaries include a convenient method called keys that makes it simple to loop through every initialized key in a dictionary ().

Remember that since Python 3, this function returns a view object rather than a list. Like its name implies, a view object is a representation of some data.

This means that while iterating through the data won't be a problem, storing the list of keys requires materialization. Which is simply accomplished by sending the view object provided to a list function Object().

Example :

my_dict = {'alpha': 5, 'beta': 4, 'gamma': 3}

# Here we're just 'looking' at the keys,
# we're not actually constructing a list
# out of them
key_view = my_dict.keys()
print("Key view:", key_view)
print("Type:", type(key_view),end="\n\n")

# Here we're materializing the keys
# into a list ofo keys
key_list = list(my_dict.keys())
print("Key list:", key_list)
print("Type: ", type(key_list),end="\n\n")

# And as we can see, view can be easily be
# used for iterating over a dictionary
for key in my_dict.keys():
    print(key, ':', my_dict[key]) 

Output:

Key view: dict_keys(['alpha', 'beta', 'gamma'])
Type: <class 'dict_keys'>

Key list: ['alpha', 'beta', 'gamma']
Type:  <class 'list'>

alpha : 5
beta : 4
gamma : 3 

Another approach might be:

my_dict = {'alpha': 5, 'beta': 4, 'gamma': 3}

for key in my_dict:
    print(key, ':', my_dict[key])

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When a dictionary is used in conjunction with the in keyword, the dictionary calls its __iter__() method. The iterator that this method returns is then used to implicitly iterate across the dictionary's keys.

Making use of the values() Method

The values() method returns a view object just like the keys() method does, but it iterates through values rather than keys :

my_dict = {'alpha': 5, 'beta': 4, 'gamma': 3}

# Inspecting the view of the values
# in the dictionary
key_list = list(my_dict.values())
print("Value list:", key_list)
print("Type: ", type(key_list), end="\n\n")

for value in my_dict.values():
    print(value, end=" ")

Output:

Value list: [5, 4, 3]
Type:  <class 'list'>
5 4 3 

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This approach merely returns values, as opposed to the prior one. When you are not worried about keys, it is helpful.

The items() method is used

The items() method returns a view object, similarly like the keys() and values() methods, but instead of only iterating through keys or values, iterates through (key,value) pairs.

Let's examine how everything functions:

my_dict = {'alpha': 5, 'beta': 4, 'gamma': 3}

# Inspecting the view of the (key,value) pairs
key_list = list(my_dict.items())
print("(key,value) pair list:", key_list)
print("Type: ", type(key_list), end="\n\n")

for item in my_dict.items():
    print(item, end=" ")

Output:

(key,value) pair list: [('alpha', 5), ('beta', 4), ('gamma', 3)]
Type:  <class 'list'>
('alpha', 5) ('beta', 4) ('gamma', 3) 

We may utilize tuple unpacking and extract both keys and values simultaneously by utilizing variables for each value in a tuple:

for key, value in my_dict.items():
    print(key,':',value)

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It is crucial to remember that in earlier versions of Python 2, the functions items(), keys(), and values() all returned copies of dictionary data. However, they return a view object in Python 3.

These are more efficient since they offer a dynamic view, and they also instantly update the view object if any changes are made to the original dictionary (and vice versa).