Working with Dictionaries

 Dictionary Methods

Python provides dictionary methods that allow us to work with dictionaries.

• copy()
• get()
• update()
• fromkeys()
   and more..

Let’s learn few among them

Referring Same Dictionary Object

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dict_a = {

'name': 'Teja',

'age': 15

}

dict_b = dict_a

dict_b['age'] = 20

print(dict_a)

print(id(dict_a))

print(id(dict_b))

PYTHON

Output

{'name':'Teja', 'age': 20}

140170705626624

140170705626624

Copy of Dictionary

dict.copy()

returns copy of a dictionary.

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dict_a = {

'name': 'Teja',

'age': 15

}

dict_b = dict_a.copy()

dict_b['age'] = 20

print(dict_a)

print(id(dict_a))

print(id(dict_b))

PYTHON

Output

{'name':'Teja', 'age': 15}

140664418952704

140664418952896

Copy of List

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list_a = ['Teja', 15]

list_b = list_a.copy()

list_b.extend([20])

print(list_a)

print(id(list_a))

print(id(list_b))

PYTHON

Output

['Teja', 15]

139631861316032

139631860589504

Operations on Dictionaries

• len()
• clear()

• Membership Check

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dict_a = {

'name': 'Teja',

'age': 15

}

print(len(dict_a)) # length of dict_a

if 'name' in dict_a: # Membership Check

print("True")

dict_a.clear() # clearing dict_a

print(dict_a)

PYTHON

Output

2

True

{}

Iterating

Cannot add/remove dictionary keys while iterating the dictionary.

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dict_a = {'name': 'Teja', 'age': 15}

for k in dict_a.keys():

if k == 'name':

del dict_a[k]

print(dict_a)

PYTHON

Output

RuntimeError: dictionary changed size during iteration

Arbitrary Function Arguments

Passing Multiple Values

We can define a function to receive any number of arguments.

We have already seen such functions

• max(*args) max(1,2,3..)
• min(*args) min(1,2,3..)

Variable Length Arguments

Variable length arguments are packed as tuple.

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def more_args(*args):

print(args)

more_args(1, 2, 3, 4)

more_args()

PYTHON

Output

(1, 2, 3, 4)

()

Unpacking as Arguments

If we already have the data required to pass to a function as a sequence, we can

unpack it with

*

while passing.

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def greet(arg1="Hi", arg2="Ram"):

print(arg1 + " " + arg2)

data = ["Hello", "Teja"]

greet(*data)

PYTHON

Output

Hello Teja

Multiple Keyword Arguments

We can define a function to receive any number of keyword arguments.

Variable length kwargs are packed as dictionary.

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def more_args(**kwargs):

print(kwargs)

more_args(a=1, b=2)

more_args()

PYTHON

Output

{'a': 1, 'b': 2}

{}

Iterating

kwargs is a dictionary. We can iterate over them like any other dictionary.

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def more_args(**kwargs):

for i, j in kwargs.items():

print('{}:{}'.format(i,j))

more_args(a=1, b=2)

PYTHON

Output

a:1

b:2

Unpacking as Arguments

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def greet(arg1="Hi", arg2="Ram"):

print(arg1 + " " + arg2)

data = {'arg1':'Hello', 'arg2':'Teja'}

greet(**data)

PYTHON

Output

Hello Teja

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def greet(arg1="Hi", arg2="Ram"):

print(arg1 + " " + arg2)

data = {'msg':'Hello', 'name':'Teja'}

greet(**data)

PYTHON

Output

TypeError: greet() got an unexpected keyword argument 'msg'