for Python dictionary

Dictionary in Python is a collection of key: value pairs, where the value is accessed using key. As dictionary is one of the data structure in Python, so we can iterate / loop through it. Consider the following to know, how you can loop through a dictionary.

for loop in dictionary Python

The 'for' loop in Python is different form the 'for' loop in the other programming languages.

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In Python, the 'for' loop does not require any update to be done. It automatically update after each iteration.

Python 'for' loop syntax

for variable in dictionary:

    statements

Directly iterating through a dictionary

If we iterate over a dictionary directly, like we have done with other data structures, by doing so we can fetch only keys.

The variable followed by in operator will represent the key in a dictionary.

Example

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for i in dic:

    print(i)

Output

one

two

three

four

five

Accessing value using keys in dictionary with for loop

While accessing value in a dictionary we make use of the key.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for i in dic:
    print(dic[i])

Output

1

2

3

4

5

Printing both key and value.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for i in dic:

    print('Key: ', i, ' - Value: ',dic[i])

Output

Key:  one  - Value:  1

Key:  two  - Value:  2

Key:  three  - Value:  3

Key:  four  - Value:  4

Key:  five  - Value:  5

Iterate through a dictionary using items() method

The items() method gives both 'key: value' pairs, so we do not have to specify the key to access a value, while iterating over a dictionary.

While iterating through a dictionary with items() method we have to specify 2 variables, the 1st one represent the key and the 2nd one represent the value in a dictionary.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for key, value in dic.items():

    print('key: ', key, ' - value: ', value)

Output

key:  one  - value:  1

key:  two  - value:  2

key:  three  - value:  3

key:  four  - value:  4

key:  five  - value:  5

Iterate through a dictionary with keys() method

The keys() method only provide the keys in a dictionary. Iterating through it will give one key at a time.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for key in dic.keys():

    print(key)

Output

one

two

three

four

five

With the provided keys, as shown above, we can access it's corresponding value.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for key in dic.keys():

    print('Key: ', key, ' - value: ', dic[key])

Output

Key:  one  - value:  1

Key:  two  - value:  2

Key:  three  - value:  3

Key:  four  - value:  4

Key:  five  - value:  5

Iterate through dictionary with values() method

When we want to fetch the values of a dictionary, we make use of value() method. 

Which will only returns the values in a dictionary, each at a time while iterating over it.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for value in dic.values():

    print(value)

Output

1

2

3

4

5

Changing values while iterating through a dictionary

Here is an example where each value is raised to the power of 2, while iterating through a dictionary.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

for value in dic.values():

    print(value**2)

Output

1

4

9

16

25

Here is how you can store the above value into a variable.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

dic2 = {}

for key, value in dic.items():

    dic2[key] = value**2

print(dic2)

Output

{'one': 1, 'two': 4, 'three': 9, 'four': 16, 'five': 25}

Filtering a dictionary while iterating through it

In this example we will filter out the odd and even numbers from the dictionary, while iterating through it.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

dic_even = {}

dic_odd = {}

for key, value in dic.items():

    if value%2==0:

        dic_even[key] = value

    else:

        dic_odd[key] = value

print('Even: ', dic_even)

print('Odd:  ', dic_odd)

Output

Even:  {'two': 2, 'four': 4}

Odd:   {'one': 1, 'three': 3, 'five': 5}

Python Dictionary comprehension

With dictionary comprehension we can do many things with just 1 line of code.

Here is, what all we can do with dictionary comprehension.

Simple formatting:-

{key: value for key, value in iterable}

Creation a dictionary with dictionary comprehension

For the creation of a dictionary with dictionary comprehension we first have to define the key: value pair in a tuple/list and then placing all the key: value pairs in a list.

Like:-

[(key, value), (key2, value2), (key3, value3), …]

And then performing dictionary comprehension, by first typing 'key: value' and then iterating through the list created as defined above.

Program

Input

LIST = [('one', 1), ('two', 2), ('three', 3)]

dic = {key: value for key, value in LIST}

print(dic)

Output

{'one': 1, 'two': 2, 'three': 3}

You can do the same by defining two list/tuples, and packing then with the zip() method.

Program

Input

LIST1 = ['one', 'two', 'three']

LIST2 = [1, 2, 3]

dic = {key: value for key, value in zip(LIST1, LIST2)}

print(dic)

Output

{'one': 1, 'two': 2, 'three': 3}

Changing keys into values and values into keys with dictionary comprehension

This example will show you, how you can flip the keys and values in a dictionary while iterating through it.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

newdic = {value: key for key, value in dic.items()}

print(newdic)

Output

{1: 'one', 2: 'two', 3: 'three', 4: 'four', 5: 'five'}

Calculations with dictionary comprehension

Following example will show you, how you can add '2' to each value of a dictionary using dictionary comprehension.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

dic = {key: value + 2 for key, value in dic.items()}

print(dic

Output

{'one': 3, 'two': 4, 'three': 5, 'four': 6, 'five': 7}

Filtering with dictionary comprehension

In this we have to specify condition after the 'for' loop.

In this example using 'if' condition we will check if a value is even, with 1st dictionary comprehension and if a value is odd, with the 2nd comprehension.

Program

Input

dic = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

dic_even = {key: value for key, value in dic.items() if value%2==0}

dic_odd = {key: value for key, value in dic.items() if value%2!=0}

print('Even dic: ', dic_even)

print('Odd dic:  ', dic_odd)

Output

Even dic:  {'two': 2, 'four': 4}

Odd dic:   {'one': 1, 'three': 3, 'five': 5}

Conclusion

Python dictionary is the collection of key: value pairs, and can be looped through it for the extraction of data.

Here we have learned how we can loop through a dictionary using for loop, fetching keys, values and both, use of items(), keys() and values() method and finally dictionary comprehension.

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