7.4. Mapping Setitem

Adds if value not exist
Updates if value exist

7.4.1. Setitem

if key is missing: adds key-value pair
if key exist: overwrites value
setitem - data[key] = value

If key is missing:

>>> data = {
...     'firstname': 'Alice',
...     'lastname': 'Apricot',
... }
>>>
>>> data['age'] = 20
>>>
>>> print(data)
{'firstname': 'Alice', 'lastname': 'Apricot', 'age': 20}

If key already exists:

>>> data = {
...     'firstname': 'Alice',
...     'lastname': 'Apricot',
...     'age': 20,
... }
>>>
>>> data['age'] = 99
>>>
>>> print(data)
{'firstname': 'Alice', 'lastname': 'Apricot', 'age': 99}

7.4.2. Update Method

if key is missing: adds key-value pair
if key exist: overwrites value
Can update multiple values at once

If key is missing:

>>> data = {
...     'firstname': 'Alice',
...     'lastname': 'Apricot',
... }
>>>
>>> data.update(age=20)
>>>
>>> print(data)
{'firstname': 'Alice', 'lastname': 'Apricot', 'age': 20}

If key already exist:

>>> data = {
...     'firstname': 'Alice',
...     'lastname': 'Apricot',
...     'age': 20,
... }
>>>
>>> data.update(age=99)
>>>
>>> print(data)
{'firstname': 'Alice', 'lastname': 'Apricot', 'age': 99}

You can update multiple values at once:

>>> data = {
...     'firstname': 'Alice',
...     'lastname': 'Apricot',
...     'age': 20,
... }
>>>
>>> data.update(age=99, group='users')
>>>
>>> print(data)
{'firstname': 'Alice', 'lastname': 'Apricot', 'age': 99, 'group': 'users'}

You can also use another dictionary to update values:

>>> data = {
...     'firstname': 'Alice',
...     'lastname': 'Apricot',
...     'age': 20,
... }
>>>
>>> data.update({'age': 99, 'group': 'users'})
>>>
>>> print(data)
{'firstname': 'Alice', 'lastname': 'Apricot', 'age': 99, 'group': 'users'}

7.4.3. Merge Operator

Merge (|) adds two dictionaries
Since Python 3.9: PEP 584 -- Add Union Operators To dict

>>> user = {
...    'firstname': 'Alice',
...    'lastname': 'Apricot',
... }
>>>
>>> permissions = {
...    'is_active': True,
...    'is_staff': True,
...    'is_admin': False,
... }
>>>
>>> result = user | permissions
>>>
>>> print(result)
{'firstname': 'Alice', 'lastname': 'Apricot', 'is_active': True, 'is_staff': True, 'is_admin': False}

7.4.4. Increment Merge Operator

Update (|=) adds right-hand dictionary to left-hand dictionary
Since Python 3.9: PEP 584 -- Add Union Operators To dict

>>> user = {
...    'firstname': 'Alice',
...    'lastname': 'Apricot',
... }
>>>
>>> permissions = {
...    'is_active': True,
...    'is_staff': True,
...    'is_admin': False,
... }
>>>
>>> user |= permissions
>>>
>>> print(user)
{'firstname': 'Alice', 'lastname': 'Apricot', 'is_active': True, 'is_staff': True, 'is_admin': False}

7.4.5. Recap

Adds if value not exist
Updates if value exist
Setitem: dict[key] = value
Update method: dict.update(key=value)
Merge operator: a | b, a |= b

7.4.6. Assignments

# %% About
# - Name: Mapping Dict Setitem
# - Difficulty: easy
# - Lines: 1
# - Minutes: 2

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Use `result: dict`
# 2. Change value for key 'age' to 20
# 3. Use setitem syntax
# 4. Run doctests - all must succeed

# %% Polish
# 1. Użyj `result: dict`
# 2. Zmień wartość dla klucza 'age' na 20
# 3. Użyj składni setitem
# 4. Uruchom doctesty - wszystkie muszą się powieść

# %% Example
# >>> result
# {'firstname': 'Alice',
#  'lastname': 'Apricot',
#  'age': 20}

# %% Hints
# - `dict[key] = value`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> from pprint import pprint

>>> assert type(result) is dict, \
'Variable `result` has an invalid type; expected: `dict`.'

>>> assert all(type(x) is str for x in result.keys()), \
'Variable `result.keys()` has elements of an invalid type; all items should be: `str`.'

>>> assert 'firstname' in result.keys()
>>> assert 'lastname' in result.keys()
>>> assert 'age' in result.keys()

>>> assert 'Alice' in result.values()
>>> assert 'Apricot' in result.values()
>>> assert None not in result.values()
>>> assert 20 in result.values()

>>> pprint(result, width=40, sort_dicts=False)
{'firstname': 'Alice',
 'lastname': 'Apricot',
 'age': 20}
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports

# %% Types
result: dict[str,str|int]

# %% Data
result = {
    'firstname': 'Alice',
    'lastname': 'Apricot',
    'age': None,
}

# %% Result

# %% About
# - Name: Mapping Dict Update
# - Difficulty: easy
# - Lines: 1
# - Minutes: 2

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Use `result: dict`
# 2. Change value for key 'age' to 99
# 3. Use `update` method
# 4. Run doctests - all must succeed

# %% Polish
# 1. Użyj `result: dict`
# 2. Zmień wartość dla klucza 'age' na 99
# 3. Użyj metody `update`
# 4. Uruchom doctesty - wszystkie muszą się powieść

# %% Example
# >>> result
# {'firstname': 'Alice',
#  'lastname': 'Apricot',
#  'age': 20}

# %% Hints
# - `dict.update(key=value)`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> from pprint import pprint

>>> assert type(result) is dict, \
'Variable `result` has an invalid type; expected: `dict`.'

>>> assert all(type(x) is str for x in result.keys()), \
'Variable `result.keys()` has elements of an invalid type; all items should be: `str`.'

>>> assert 'firstname' in result.keys()
>>> assert 'lastname' in result.keys()
>>> assert 'age' in result.keys()

>>> assert 'Alice' in result.values()
>>> assert 'Apricot' in result.values()
>>> assert None not in result.values()
>>> assert 20 in result.values()

>>> pprint(result, width=40, sort_dicts=False)
{'firstname': 'Alice',
 'lastname': 'Apricot',
 'age': 20}
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports

# %% Types
result: dict[str,str|int]

# %% Data
result = {
    'firstname': 'Alice',
    'lastname': 'Apricot',
    'age': None,
}

# %% Result

# %% About
# - Name: Mapping Dict UpdateMany
# - Difficulty: easy
# - Lines: 1
# - Minutes: 2

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Modify `result: dict`:
#    - change value for key 'firstname' to 'Bob'
#    - change value for key 'lastname' to 'Blackthorn'
# 2. Use `update` method
# 3. Run doctests - all must succeed

# %% Polish
# 1. Zmodyfikuj `result: dict`:
#    - zmień wartość dla klucza 'firstname' na 'Bob'
#    - zmień wartość dla klucza 'lastname' na 'Blackthorn'
# 2. Użyj metodę `update`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Hints
# - `dict.update()`

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> from pprint import pprint

>>> assert type(result) is dict, \
'Variable `result` has an invalid type; expected: `dict`.'

>>> assert all(type(x) is str for x in result.keys()), \
'Variable `result.keys()` has elements of an invalid type; all items should be: `str`.'

>>> assert 'firstname' in result.keys()
>>> assert 'lastname' in result.keys()
>>> assert 'group' in result.keys()

>>> assert 'Alice' not in result.values()
>>> assert 'Apricot' not in result.values()

>>> assert 'Bob' in result.values()
>>> assert 'Blackthorn' in result.values()
>>> assert 'users' in result.values()

>>> pprint(result, width=40, sort_dicts=False)
{'firstname': 'Bob',
 'lastname': 'Blackthorn',
 'group': 'users'}
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports

# %% Types
result: dict[str,str]

# %% Data
result = {
    'firstname': 'Alice',
    'lastname': 'Apricot',
    'group': 'users',
}

# %% Result

# %% About
# - Name: Mapping Dict Union
# - Difficulty: easy
# - Lines: 1
# - Minutes: 2

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% English
# 1. Use `DATA_A: dict`
# 2. Use `DATA_B: dict`
# 3. Define `result: dict` with union of `DATA_A` and `DATA_B`
# 4. Run doctests - all must succeed

# %% Polish
# 1. Użyj `DATA_A: dict`
# 2. Użyj `DATA_B: dict`
# 3. Zdefiniuj `result: dict` z unią `DATA_A` i `DATA_B`
# 4. Uruchom doctesty - wszystkie muszą się powieść

# %% Exp

# %% Hints
# - `|` - "or" operator

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> from pprint import pprint
>>> import string

>>> assert result is not Ellipsis, \
'Variable `result` has an invalid value; assign result of your program to it.'

>>> assert type(result) is dict, \
'Variable `result` has an invalid type; expected: `dict`.'

>>> pprint(result, width=40, sort_dicts=True)
{'alice': 'Alice Apricot',
 'bob': 'Bob Blackthorn',
 'carol': 'Carol Corn',
 'dave': 'Dave Durian',
 'eve': 'Eve Elderberry',
 'mallory': 'Mallory Melon'}
"""

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -f -v myfile.py`

# %% Imports

# %% Types
result: dict[str, str]

# %% Data
DATA_A = {
    'alice': 'Alice Apricot',
    'bob': 'Bob Blackthorn',
    'carol': 'Carol Corn',
}

DATA_B = {
    'dave': 'Dave Durian',
    'eve': 'Eve Elderberry',
    'mallory': 'Mallory Melon',
}

# %% Result
result = ...