Python Design Patterns - Dictionaries


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Dictionaries are the data structures, which include a key value combination. These are widely used in place of JSON – JavaScript Object Notation. Dictionaries are used for API (Application Programming Interface) programming. A dictionary maps a set of objects to another set of objects. Dictionaries are mutable; this means they can be changed as and when needed based on the requirements.

How to implement dictionaries in Python?

The following program shows the basic implementation of dictionaries in Python starting from its creation to its implementation.

# Create a new dictionary
d = dict() # or d = {}

# Add a key - value pairs to dictionary
d['xyz'] = 123
d['abc'] = 345

# print the whole dictionary
print(d)

# print only the keys
print(d.keys())

# print only values
print(d.values())

# iterate over dictionary
for i in d :
   print("%s %d" %(i, d[i]))
	
# another method of iteration
for index, value in enumerate(d):
   print (index, value , d[value])

# check if key exist 23. Python Data Structure –print('xyz' in d)

# delete the key-value pair
del d['xyz']

# check again
print("xyz" in d)

Output

The above program generates the following output −

Dictionaries

Note −There are drawbacks related to the implementation of dictionaries in Python.

Drawback

Dictionaries do not support the sequence operation of the sequence data types like strings, tuples and lists. These belong to the built-in mapping type.



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