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'
}
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'}
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']
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))
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}")
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
intorfloat, frequency is the number of digits. Keep the keys of the old as the new.
Summary
- is a
key-valuepair sequence - is of structure,
my_dict = {key:value} -
dict(name='name')casts to a dict - dict_obj[
key] returns thevalueatkey -
dict_obj[key] = valueto create new item in dictionary or update - loop through dictionary by keys, values and items
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