Dictionaries in Python
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This document provides information about dictionaries in Python. It defines dictionaries as mutable containers that store key-value pairs, with keys being unique and values being of any type. It describes dictionary syntax and how to access, update, delete and add elements. It notes that dictionary keys must be immutable like strings or numbers, while values can be any type. Properties of dictionary keys like no duplicate keys and keys requiring immutability are also summarized.
![Accessing Values in Dictionary:
● To access dictionary elements, you can use the familiar
square brackets along with the key to obtain its value.
● For example:
● dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
print "dict['Name']: ", dict['Name'];
● Output:
dict['Name']: Zara](https://image.slidesharecdn.com/dictionaries-130820012026-phpapp02/85/Dictionaries-in-Python-8-320.jpg)
![Updating Dictionary:
●You can update a dictionary by adding a new entry or item (i.e., a key-value pair)
I.e:
●modifying an existing entry, or deleting an existing entry as shown below in the
simple example
●dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
dict['Age'] = 8; # update existing entry
dict['School'] = "DPS School"; # Add new entry
print "dict['Age']: ", dict['Age'];
print "dict['School']: ", dict['School'];
●Output:
dict['Age']: 8
●dict['School']: DPS School](https://image.slidesharecdn.com/dictionaries-130820012026-phpapp02/85/Dictionaries-in-Python-9-320.jpg)
![Delete Dictionary Elements:
You can either remove individual dictionary elements or clear the entire
contents of a dictionary
● To explicitly remove an entire dictionary, just use the del statement.
i.e:
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
● del dict['Name']; # remove entry with key 'Name'
dict.clear(); # remove all entries in dict
del dict ; # delete entire dictionary
● print "dict['Age']: ", dict['Age'];
● print "dict['School']: ", dict['School'];
output:dict['Age']:
Traceback (most recent call last):
File "test.py", line 8, in <module>
print "dict['Age']: ", dict['Age'];
TypeError: 'type' object is unsubscriptable](https://image.slidesharecdn.com/dictionaries-130820012026-phpapp02/85/Dictionaries-in-Python-10-320.jpg)
![Properties of Dictionary Keys:
● There are two important points to remember about dictionary keys:
● (a) More than one entry per key not allowed. Which means no duplicate key is allowed.
When duplicate keys encountered during assignment, the last assignment wins.
● i.e:
● dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'};
print "dict['Name']: ", dict['Name'];
● Output:
● dict['Name']: Manni
● (b) Keys must be immutable. Which means you can use strings, numbers, or tuples as
dictionary keys but something like ['key'] is not allowed. Following is a simple example:
● dict = {['Name']: 'Zara', 'Age': 7};
● print "dict['Name']: ", dict['Name']; output:Traceback (most recent call last):
File "test.py", line 3, in <module>
ict = {['Name']: 'Zara', 'Age': 7};
TypeError: list objects are unhashable](https://image.slidesharecdn.com/dictionaries-130820012026-phpapp02/85/Dictionaries-in-Python-11-320.jpg)
Dictionaries in Python
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- 6. Python Dictionary: ● A dictionary is mutable and is another container type that can store any number of Python objects ● Dictionaries consist of pairs (called items) of keys and their corresponding values. ● Python dictionaries are also known as associative arrays or hash tables. ● The general syntax of a dictionary is as follows: ● dict = {'A': '2341', 'B': '9102', 'C': '3258'}
- 7. Python Dictionary Features: ● Each key is separated from its value by a colon (:). ● The items are separated by commas, and the whole thing is enclosed in curly braces. ● An empty dictionary without any items is written with just two curly braces, like this: {}. ● Keys are unique within a dictionary while values may not be ● The values of a dictionary can be of any type, but the keys must be of an immutable data type such as strings, numbers, or tuples.
- 8. Accessing Values in Dictionary: ● To access dictionary elements, you can use the familiar square brackets along with the key to obtain its value. ● For example: ● dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}; print "dict['Name']: ", dict['Name']; ● Output: dict['Name']: Zara
- 9. Updating Dictionary: ●You can update a dictionary by adding a new entry or item (i.e., a key-value pair) I.e: ●modifying an existing entry, or deleting an existing entry as shown below in the simple example ●dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}; dict['Age'] = 8; # update existing entry dict['School'] = "DPS School"; # Add new entry print "dict['Age']: ", dict['Age']; print "dict['School']: ", dict['School']; ●Output: dict['Age']: 8 ●dict['School']: DPS School
- 10. Delete Dictionary Elements: You can either remove individual dictionary elements or clear the entire contents of a dictionary ● To explicitly remove an entire dictionary, just use the del statement. i.e: dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}; ● del dict['Name']; # remove entry with key 'Name' dict.clear(); # remove all entries in dict del dict ; # delete entire dictionary ● print "dict['Age']: ", dict['Age']; ● print "dict['School']: ", dict['School']; output:dict['Age']: Traceback (most recent call last): File "test.py", line 8, in <module> print "dict['Age']: ", dict['Age']; TypeError: 'type' object is unsubscriptable
- 11. Properties of Dictionary Keys: ● There are two important points to remember about dictionary keys: ● (a) More than one entry per key not allowed. Which means no duplicate key is allowed. When duplicate keys encountered during assignment, the last assignment wins. ● i.e: ● dict = {'Name': 'Zara', 'Age': 7, 'Name': 'Manni'}; print "dict['Name']: ", dict['Name']; ● Output: ● dict['Name']: Manni ● (b) Keys must be immutable. Which means you can use strings, numbers, or tuples as dictionary keys but something like ['key'] is not allowed. Following is a simple example: ● dict = {['Name']: 'Zara', 'Age': 7}; ● print "dict['Name']: ", dict['Name']; output:Traceback (most recent call last): File "test.py", line 3, in <module> ict = {['Name']: 'Zara', 'Age': 7}; TypeError: list objects are unhashable
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