Dictionary in Python |

 

Python Dictionaries

Dictionaries are used to store data values in key:value pairs.

A dictionary is a collection which is ordered*, changeable and do not allow duplicates.

As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered

Dictionaries are written with curly brackets, and have keys and values:

Example

Create and print a Dictionary

d = {
  "brand": "Honda",
  "model": "City",
  "year": 1964
}
print(d)

Output:

{'brand': ‘Honda’, 'model': ‘City, 'year': 1964}

Iterate Dictionary Items

Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

Example

Print the "brand" value of the dictionary:

d = {
  "brand": "Honda",
  "model": "City",
  "year": 1964
}
print(d["brand"])

Output:

Honda

Iterate Dictionary All Items

Dictionary items are presented in key:value pairs, and can be referred to by using the for loop.

Example

Print the "brand" value of the dictionary:

d = {
  "brand": "Honda",
  "model": "City",
  "year": 1964
}

for x in d:
print(d["x"])

Output:

Honda

City

1964

Duplicates Not Allowed

Dictionaries cannot have two items with the same key:

Example

Duplicate values will overwrite existing values:

d = {
  "brand": "Honda",
  "model": "City",
  "year": 1964,

  "year": 1980
}
print(d)

Output:

{'brand': ‘Honda’, 'model': ‘City, 'year': 1980}

Dictionary Length

To determine how many items a dictionary has, use the len() function:

Example

Print the number of items in the dictionary:

d = {
  "brand": "Honda",
  "model": "City",
  "year": 1964,

}
print(len(d))

Output:

3

type()

From Python's perspective, dictionaries are defined as objects with the data type 'dict':

<class 'dict'>

Example

Print the data type of a dictionary:

d = {
  "brand": "Honda",
  "model": "City",
  "year": 1964,

}
print(type(d))

Output:

<class 'dict'>

Dictionary Items - Data Types

The values in dictionary items can be of any data type:

Example

String, int, boolean, and list data types:

d = {
  "brand": "Honda",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

print(d)

Output:

{'brand': ‘Honda, 'electric': False, 'year': 1964, 'colors': ['red', 'white', 'blue']}

The dict() Constructor

It is also possible to use the dict() constructor to make a dictionary.

Example

Using the dict() method to make a dictionary:

d = dict(name = "Manoj", age = 36, country = "India")
print(d)

Output:

{'name': ‘Manoj’, 'age': 36, 'country': ‘India’}

Python Collections (Arrays)

There are four collection data types in the Python programming language:

1.       List is a collection which is ordered and changeable. Allows duplicate members.

2.       Tuple is a collection which is ordered and unchangeable. Allows duplicate members.

3.       Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.

4.       Dictionary is a collection which is ordered** and changeable. No duplicate members.

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