*Memos:
- My post explains dictionary (2) and copy.
- My post explains the useful functions for a dictionary (1).
- My post explains the useful functions for a dictionary (2).
- My post explains the shallow and deep copy of a dictionary.
- My post explains a list and the list with indexing.
- My post explains a tuple.
- My post explains a set and copy.
- My post explains an iterator (1).
- My post explains variable assignment.
A dictionary:
- is the ordered collection with zero or more pairs of
key:valueto use non-huge data not to getMemoryError. - doesn't allow duplicated keys (even with different types). *The values of the last duplicated keys are used.
- is mutable so it can be changed.
- can have any mixed types of keys and values except a list, set and dictionary for a key.
- can be used like a list.
- can be unpacked with
**. - cannot be enlarged with
*and a number. - can be created by
{}, a dictionary(dict) comprehension or dict() with or without a dictionary. *dict()cannot create a dictionary with a list, tuple, set, iterator, string or range(). - can be accessed and changed by keying and indexing.
- cannot be accessed and changed by slicing properly.
- can be continuously used through multiple variables.
- can be copied to refer to a different dictionary.
A dictionary is for non-huge data otherwise it gets MemoryError.
{} can create a dictionary as shown below:
v = {} # Empty 1D dictionary
v = {'name':'John', 'age':36} # 1D dictionary
v = dict(name='John', age=36) # 1D dictionary
v = dict([('name', 'John'), ('age', 36)]) # 1D dictionary
v = {'name':'John', 'age':36, 'name':'Anna', 'age':24} # 1D dictionary
v = {'person1':{'name':'John', 'age':36}, # 2D dictionary
'person2':{'name':'Anna', 'age':24}}
v = dict(person1=dict(name='John', age=36), # 2D dictionary
person2=dict(name='Anna', age=24))
v = dict([('person1', dict([('name', 'John'), ('age', 36)])), # 2D dictionary
('person2', dict([('name', 'Anna'), ('age', 24)]))])
v = {1:'a', 1.0:'b', 1.0+0.0j:'c', True:'d'}
v = {'a':'b', 2:3, 2.3:4.5, 2.3+4.5j:6.7+8.9j, True:False,
'l':[4, 5], (2, 3):(4, 5), 's':{4, 5}, 'd':{'c':'d'}}
v = {'':'abc', ():(1, 2, 3)}
v = {0:'apple', 1:'orange', 2:'kiwi'} # 1D dictionary
# No error
v = {[2, 3]:[4, 5]}
# TypeError: unhashable type: 'list'
v = {{'a':'b'}:{'c':'d'}}
# TypeError: unhashable type: 'dict'
v = {{2, 3}:{4, 5}}
# TypeError: unhashable type: 'set'
v = {'name':'John', 'age':36} * 3
# TypeError: unsupported operand type(s) for *: 'dict' and 'int'
A dictionary is the ordered collection with zero or more pairs of key:value as shown below:
v = {'name':'John', 'age':36}
print(v) # {'name': 'John', 'age': 36}
A dictionary doesn't allow duplicated keys (even with different types) as shown below. *The values of the last duplicated keys are used:
v = {'name':'John', 'age':36, 'name':'Anna', 'age':24}
print(v) # {'name': 'Anna', 'age': 24}
v = {1:'a', 1.0:'b', 1.0+0.0j:'c', True:'d'}
print(v) # {1: 'd'}
A dictionary can have any mixed types of values except a list, set and dictionary for a key as shown below:
v = {'a':'b', 2:3, 2.3:4.5, 2.3+4.5j:6.7+8.9j, True:False,
'l':[4, 5], (2, 3):(4, 5), 's':{4, 5}, 'd':{'c':'d'}}
print(v)
# {'a': 'b', 2: 3, 2.3: 4.5, (2.3+4.5j): (6.7+8.9j), True: False,
# 'l': [4, 5], (2, 3): (4, 5), 's': {4, 5}, 'd': {'c': 'd'}}
print(v[2], v[2.3], v[2.3+4.5j], v[True], v[(2,3)])
# 3 4.5 (6.7+8.9j) False (4, 5)
v = {'':'abc', ():(1, 2, 3)}
print(v[''], v[()])
# abc (1, 2, 3)
You can use a dictionary 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], v[1], v[2]) # APPLE ORANGE KIWI
v[0:2] = ['banana', 'peach']
print(v[0], v[1], v[2], v[0:2])
# apple orange kiwi ['banana', 'peach']
** can unpack a dictionary as shown below:
v1 = {"fname":"John", "lname":"Smith"}
v2 = {"age":36, "gender":"Male"}
v3 = {**v1, **v2}
print(v3) # {'fname': 'John', 'lname': 'Smith', 'age': 36, 'gender': 'Male'}
A dictionary(dict) comprehension can create a dictionary as shown below:
v = {x:x**2 for x in range(6)}
print(v) # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}