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Michael Otu
Michael Otu

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Python3 Programming - Exercise 17 - Dictionary

#python3 #tutorial #beginners #programming

Dictionary

A dictionary just like a list, tuple and a set which is a sequence. A dictionary is rather key-value pair. String, list, etc are number-indexed. A dictionary is key-indexed.

Structure of a dictionary 

# dict_var = { key : value }  # empty dictionary my_dict = {} # profile dictionary profile = { 'name': 'John Doe', 'age': 32, 'job': 'Software engineer' }
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Casting

Casting is done with dict()

# passing a keyword and a value  # dict(key-word=value, ... ) my_dict = dict( name='John Doe', age=32, job='Software engineer' ) # convert a list of tuple to a dictionary my_tupled_list = [('name', 'John Doe'), ('age', 32, ), ('job', 'Software engineer')] my_dict = dict(my_tupled_list) print(my_tupled_list) # output-> # {'name': 'John Doe', 'age': 32, 'job': 'Software engineer'}
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Indexing and updating a dictionary

Indexing and updating are done just as we would do to a list.

# consider this dictionary profile = { 'name': 'John Doe', 'age': 32, 'job': 'Software engineer' } # get the name and job name = profile['name'] job = profile['job'] print(f"Candidates name is {name} and works, {job}") # update the age profile['age'] = 30 # add a new key profile['lang'] = 'Python' # delete a key to delete a value using - del del profile['age']
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dictionary functions

Functions description
clear deletes all the items in the dictionary, similar to reassigning it to dict()
copy returns a copy of the dictionary
get( key , default value ) returns a value of that key just like dict_object[key] but returns default value when key doesn't exist. This does not update the dictionary
items returns the items in the dictionary
values returns the values of the dictionary
keys returns the keys of the dictionary
pop( key ) deletes item with the key just like del
popitem deletes the last item in the dictionary
setdefault( key , value ) adds key value to dictionary if key doesn't exist, unlike get

Examples 

# empty dict profile = dict() # add an item - 3 ways use any profile['name'] = 'John Doe' # we use this more - simplier  profile.update(age=32) profile.setdefault('job', 'Software engineer') print(profile) # get an item from the dict  # get the keys from a dictionary profile_keys = profile.keys() print(profile_keys) # output-> dict_keys(['name', 'age', 'job'])  # get the values from a dictionary profile_values = profile.values() print(profile_values) # output-> dict_values(['John Doe', 32, 'Software engineer'])  # get the key and value as items profile_content = profile.items() print(profile_content) # do the printing  # get element by key username = profile['name'] print(f"user name: {username}") # what if the key doesn't exist # use get with default value # profile['height'] -> KeyError height = profile.get('height', 130) print(height) # -> 130  # but height won't be added to the dict # use set default, update or dict[key] = value if not 'height' in profile.keys(): # any of this would work  profile['height'] = 120 # profile.update(height = 120)  # profile.setdefault('height', 120) else: print('Profile updated, height added') print(profile) # copy new_profile = profile.copy() print(new_profile) # pop - remove height profile.pop('height') # or # del profile['height']  # delete all items in the dict profile.popitem() print(len(new_profile) == len(profile))
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Looping through a dictionary

Looping is the same everywhere in a list, set and tuple, in even a string, but for a dictionary, we may loop using a key or and value.

# consider this sample dictionary profile = { 'name': 'John Doe', 'age': 32, 'job': 'Software engineer' } # looping through keys for key in profile.keys(): print(f"key: {key}") # looping through values for value in profile.values(): print(f"value: {value}") # looping through the items in the dictionary # we loop through the key and value at the same time for key, value in profile.items(): print(f"{key} has a value of {value}")
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Practicals

  • Write a function that removes items with duplicate values
  • Write a function that takes a dictionary as an argument, return another dictionary that has the frequency of the length of the value, if value is int or float, frequency is the number of digits. Keep the keys of the old as the new.

Summary

  • is a key-value pair sequence
  • is of structure, my_dict = {key:value}
  • dict(name='name') casts to a dict
  • dict_obj[ key ] returns the value at key
  • dict_obj[key] = value to create new item in dictionary or update
  • loop through dictionary by keys, values and items

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