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Super Kai (Kazuya Ito)
Super Kai (Kazuya Ito)

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Dictionary functions in Python (3)

#python #dictionary #mutable #function

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*Memo:

  • My post explains dictionary functions (1).
  • My post explains dictionary functions (2).
  • My post explains a dictionary (1).

fromkeys() can create a dictionary with pairs of a key and default value as shown below:

*Memo:

  • The 1st argument is iterable(Required-Type:Iterable):
    • Don't use iterable=.
  • The 2nd argument is value(Optional-Default:None-Type:Any) to set its default value with the keys of iterable:
    • Don't use value=. 
# 1D dictionary print(dict.fromkeys(['A', 'B', 'C'])) print(dict.fromkeys(['A', 'B', 'C'], None)) # {'A': None, 'B': None, 'C': None}  # 1D dictionary print(dict.fromkeys(['A', 'B', 'C'], 'X')) # {'A': 'X', 'B': 'X', 'C': 'X'}  # 2D dictionary print(dict.fromkeys(['A', 'B', 'C'], {'X':'Y'})) # {'A': {'X': 'Y'}, 'B': {'X': 'Y'}, 'C': {'X': 'Y'}}  # 3D dictionary print(dict.fromkeys(['A', 'B', 'C'], {'X':{'Y':'Z'}})) # {'A': {'X': {'Y': 'Z'}}, 'B': {'X': {'Y': 'Z'}}, 'C': {'X': {'Y': 'Z'}}}
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sorted() can convert a dictionary to the list which has the zero or more keys and/or values of the dictionary, then sort the list as shown below:

*Memo:

  • The 1st argument is iterable(Required-Type:Iterable):
    • Don't use iterable=.
  • The 2nd argument is key(Optional-Default:None-Type:Callable/NoneType).
  • The 3rd argument is reverse(Optional-Default:False) to reverse the list.
  • By default, the list which has the zero or more keys of a dictionary is used.
  • sorted() creates a copy:
    • Be careful, sorted() does shallow copy instead of deep copy as my issue.

<1D dictionary>: 

v = {'name':'John', 'age':36} print(sorted(v)) print(sorted(v, key=None, reverse=False)) print(sorted(v.keys())) # ['age', 'name']  print(sorted(v.values(), key=lambda key: str(key))) # [36, 'John']  print(sorted(v.items())) # [('age', 36), ('name', 'John')]  print(sorted(v, reverse=True)) print(sorted(v.keys(), reverse=True)) # ['name', 'age']  print(sorted(v.values(), key=lambda key: str(key), reverse=True)) # ['John', 36]  print(sorted(v.items(), reverse=True)) # [('name', 'John'), ('age', 36)]
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<2D dictionary>: 

v = {'person1':{'name':'John', 'age':36}, 'person2':{'name':'Anna', 'age':24}} print(sorted(v)) print(sorted(v.keys())) # ['person1', 'person2']  print(sorted(v.values(), key=lambda key: str(key))) # [{'name': 'Anna', 'age': 24}, # {'name': 'John', 'age': 36}]  print(sorted(v.items())) # [('person1', {'name': 'John', 'age': 36}), # ('person2', {'name': 'Anna', 'age': 24})]  print(sorted(v, reverse=True)) print(sorted(v.keys(), reverse=True)) # ['person2', 'person1']  print(sorted(v.values(), key=lambda key: str(key), reverse=True)) # [{'name': 'John', 'age': 36}, # {'name': 'Anna', 'age': 24}]  print(sorted(v.items(), reverse=True)) # [('person2', {'name': 'Anna', 'age': 24}), # ('person1', {'name': 'John', 'age': 36})]  print(sorted(v['person2'])) print(sorted(v['person2'].keys())) # ['age', 'name']  print(sorted(v['person2'].values(), key=lambda key: str(key))) # [24, 'Anna']  print(sorted(v['person2'].items())) # [('age', 24), ('name', 'Anna')]  print(sorted(v['person2'], reverse=True)) print(sorted(v['person2'].keys(), reverse=True)) # ['name', 'age']  print(sorted(v['person2'].values(), key=lambda key: str(key), reverse=True)) # ['Anna', 24]  print(sorted(v['person2'].items(), reverse=True)) # [('name', 'Anna'), ('age', 24)]
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reversed() can return the iterator which has the reversed zero or more keys and/or values of a dictionary, then the iterator is converted to a list with list() as shown below:

*Memo:

  • The 1st argument is seq(Required:Type-Sequence):
    • Don't use seq=.
  • By default, the list which has the zero or more keys of a dictionary is used.

<1D dictionary>: 

v = {'name':'John', 'age':36} print(reversed(v)) # <dict_reversekeyiterator object at 0x000001F3B9E51530>  print(list(reversed(v))) print(list(reversed(v.keys()))) # ['age', 'name']  print(list(reversed(v.values()))) # [36, 'John']  print(list(reversed(v.items()))) # [('age', 36), ('name', 'John')]
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<2D dictionary>: 

v = {'person1':{'name':'John', 'age':36}, 'person2':{'name':'Anna', 'age':24}} print(list(reversed(v))) print(list(reversed(v.keys()))) # ['person2', 'person1']  print(list(reversed(v.values()))) # [{'name': 'Anna', 'age': 24}, # {'name': 'John', 'age': 36}]  print(list(reversed(v.items()))) # [('person2', {'name': 'Anna', 'age': 24}), # ('person1', {'name': 'John', 'age': 36})]  print(list(reversed(v['person2']))) print(list(reversed(v['person2'].keys()))) # ['age', 'name']  print(list(reversed(v['person2'].values()))) # [24, 'Anna']  print(list(reversed(v['person2'].items()))) # [('age', 24), ('name', 'Anna')]
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