Dictionary in Python (9)

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*Memo:

• My post explains a dictionary (1).
• My post explains a dictionary (2).
• My post explains a dictionary (3).
• My post explains a dictionary (4).
• My post explains a dictionary (5).
• My post explains a dictionary (6).
• My post explains a dictionary (7).
• My post explains a dictionary (8).

A dictionary can be read or changed by keying and a del statement as shown below:

*Memo:

• Keying can be done with one or more [key]:
  • key(Required-Type:Hashable):
    • Don't use key=.
  • Error occurs if key doesn't exist.
• A del statement can remove one or more pairs of a key and value from a dictionary by keying and can remove one or more variables themselves.

<1D dictionary>:

v = {'name':'John', 'age':36}
v = dict(name='John', age=36)
v = dict([('name', 'John'), ('age', 36)])

print(v['name'], v['age'])
# John 36

v['name'] = 'Emily'
v['gender'] = 'Female'

v['name'], v['gender'] = 'Emily', 'Female'

print(v)
# {'name': 'Emily', 'age': 36, 'gender': 'Female'}

del v['name'], v['gender']

print(v)
# {'age': 36}

del v

print(v)
# NameError: name 'v' is not defined

v = {'name':'John', 'age':36}

print(v['gender'])
del v['gender']
# KeyError: 'gender'

<2D dictionary>:

v = {'person1':{'name':'John', 'age':36},
     'person2':{'name':'Anna', 'age':24}}
v = dict(person1=dict(name='John', age=36),
         person2=dict(name='Anna', age=24))
v = dict([('person1', dict([('name', 'John'), ('age', 36)])),
          ('person2', dict([('name', 'Anna'), ('age', 24)]))])

print(v['person1'], v['person2'])
# {'name': 'John', 'age': 36} {'name': 'Anna', 'age': 24}

print(v['person1']['name'], v['person1']['age'],
      v['person2']['name'], v['person2']['age'])
# John 36 Anna 24

v['person1']['name'] = 'Emily'
v['person2']['gender'] = 'Female'
v['person3'] = {'name':'Peter', 'age':18, 'gender':'Male'}

print(v)
# {'person1': {'name': 'Emily', 'age': 36},
#  'person2': {'name': 'Anna', 'age': 24, 'gender': 'Female'},
#  'person3': {'name': 'Peter', 'age': 18, 'gender': 'Male'}}

del v['person1']
del v['person3']['name'], v['person3']['gender']

print(v)
# {'person2': {'name': 'Anna', 'age': 24, 'gender': 'Female'},
#  'person3': {'age': 18}}

<3D dictionary>:

v = {'person1':{'name':{'fname':'John', 'lname':'Smith'}},
     'person2':{'name':{'fname':'Anna', 'lname':'Brown'}}}
v = dict(person1=dict(name=dict(fname='John', lname='Smith')),
         person2=dict(name=dict(fname='Anna', lname='Brown')))
v = dict([('person1', dict([('name', dict([('fname', 'John'),
                                           ('lname', 'Smith')]))])),
          ('person2', dict([('name', dict([('fname', 'Anna'),
                                           ('lname', 'Brown')]))]))])
print(v['person1'], v['person2'])
# {'name': {'fname': 'John', 'lname': 'Smith'}}
# {'name': {'fname': 'Anna', 'lname': 'Brown'}}

print(v['person1']['name'], v['person2']['name'])
# {'fname': 'John', 'lname': 'Smith'}
# {'fname': 'Anna', 'lname': 'Brown'}

v['person1']['name']['fname'] = 'Emily'
v['person1']['name']['mname'] = 'Lee'
v['person2']['gender'] = 'Female'
v['person3'] = {'name':{'fname':'Peter', 'lname':'Davis'},
                'gender':'Male'}
print(v)
# {'person1': {'name': {'fname': 'Emily', 'lname': 'Smith',
#              'mname': 'Lee'}},
#  'person2': {'name': {'fname': 'Anna', 'lname': 'Brown'},
#              'gender': 'Female'},
#  'person3': {'name': {'fname': 'Peter', 'lname': 'Davis'},
#              'gender': 'Male'}}

del v['person1']
del v['person2']['name']
del v['person3']['name']['lname'], v['person3']['gender']

print(v)
# {'person2': {'gender': 'Female'},
#  'person3': {'name': {'fname': 'Peter'}}}

A dictionary can be used like a list by indexing but not by slicing properly as shown below:

v = {0:'apple', 1:'orange', 2:'kiwi'}

print(v[0], v[1], v[2])
# Apple Orange Kiwi

v[0] = 'APPLE'
v[1] = 'ORANGE'
v[2] = 'KIWI'

print(v)
# {0: 'APPLE', 1: 'ORANGE', 2: 'KIWI'}

v[0:2] = ['banana', 'peach']

print(v)
# {0: 'APPLE', 1: 'ORANGE', 2: 'KIWI', slice(0, 2, None): ['banana', 'peach']}

A dictionary can be continuously used through multiple variables as shown below:

v1 = v2 = v3 = {'name':'John', 'age':36, 'gender':'Male'}
                        # Equivalent
                        # v1 = {'name':'John', 'age':36, 'gender':'Male'}
                        # v2 = v1
                        # v3 = v2
v1['name'] = 'Anna'
v2['age'] = 24
v3['gender'] = 'Female'

print(v1) # {'name': 'Anna', 'age': 24, 'gender': 'Female'}
print(v2) # {'name': 'Anna', 'age': 24, 'gender': 'Female'}
print(v3) # {'name': 'Anna', 'age': 24, 'gender': 'Female'}

A dictionary can be shallow-copied and deep-copied as shown below:

<Shallow copy>:

*Memo:

• v1 and v2 refer to different outer dictionaries and the same inner dictionary.
• is can check if v1 and v2 refer to the same outer and inner dictionary.
• dict.copy(), copy.copy() and dict() shallow-copy a dictionary:
  • dict.copy() has no arguments.

import copy

v1 = {'a':'b', 'c':{'d':'e'}}
v2 = v1.copy()
v2 = copy.copy(v1)
v2 = dict(v1)

print(v1) # {'a': 'b', 'c': {'d': 'e'}}
print(v2) # {'a': 'b', 'c': {'d': 'e'}}

print(v1 is v2, v1['c'] is v2['c'])
# False True

v2['a'] = 'X'
v2['c']['d'] = 'Y'
          #       ↓↓↓             ↓↓↓
print(v1) # {'a': 'b', 'c': {'d': 'Y'}}
print(v2) # {'a': 'X', 'c': {'d': 'Y'}}
          #       ↑↑↑             ↑↑↑

<Deep copy>:

*Memo:

• v1 and v2 refer to different outer and inner dictionaries.

*Memo:

• copy.deepcopy() deep-copies a dictionary.
• copy.deepcopy() should be used because it's safe, deeply copying a dictionary while dict.copy(), copy.copy() and dict() aren't safe, shallowly copying a dictionary.

import copy

v1 = {'a':'b', 'c':{'d':'e'}}
v2 = copy.deepcopy(v1)

print(v1) # {'a': 'b', 'c': {'d': 'e'}}
print(v2) # {'a': 'b', 'c': {'d': 'e'}}

print(v1 is v2, v1['c'] is v2['c'])
# False False

v2['a'] = 'X'
v2['c']['d'] = 'Y'
          #       ↓↓↓             ↓↓↓
print(v1) # {'a': 'b', 'c': {'d': 'e'}}
print(v2) # {'a': 'X', 'c': {'d': 'Y'}}
          #       ↑↑↑             ↑↑↑