10.3. While Break

Force exit the loop

10.3.1. Syntax

>>> while True:
...     break

10.3.2. Example

>>> i = 0
>>>
>>> while True:
...     print(i)
...     i += 1
...     if i == 3:
...         break
0
1
2

10.3.3. Use Case - 1

Force user to respond
If answer is not 'yes' or 'no' ask again

>>> 
... while True:
...     answer = input('Continue [yes/no]?')
...     if answer in ('yes', 'no'):
...         break

10.3.4. Use Case - 2

If user hit enter key, without typing a number
Variable number will be equal to '' (empty string)
Keyword break will exit the loop

>>> 
... while True:
...     number = input('Type number: ')
...
...     if not number:
...         break

If user hit enter key without typing a number, variable number will be equal to '' (empty string). Logic value of empty string is False, therefore it will execute the if block content. Keyword break will exit the loop.

10.3.5. Use Case - 3

>>> i = 10
>>>
>>> while True:
...     print(i)
...     i -= 1
...
...     if i == 6:
...         print('Fuel leak detected. Abort, Abort, Abort!')
...         break
10
9
8
7
Fuel leak detected. Abort, Abort, Abort!

10.3.6. Assignments

# TODO: Write automated tests

# %% 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

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

# %% About
# - Name: While Break Guessing
# - Difficulty: medium
# - Lines: 9
# - Minutes: 5

# %% English
# 1. Use `input` in `while True` loop to ask user about number
# 2. Compare user's number with `HIDDEN`:
#    - If number is equal, print `Exactly` and break game
#    - If number is greater, print `Above`
#    - If number is lower, print `Below`
# 3. Non-functional requirements:
#    - User will always input only one digit
#    - User will not input any invalid characters or longer numbers
#    - `Mock` will simulate inputting numbers by a user
#    - Use `input()` function as normal
# 4. Run doctests - all must succeed

# %% Polish
# 1. Użyj `input` w pętli `while True` do pytania użytkownika o liczbę
# 2. Porównaj liczbę wprowadzoną przez użytkownika z `HIDDEN`:
#    - Jeżeli jest taka sama, to wypisz `Exactly` i zakończ grę
#    - Jeżeli jest większa, to wypisz `Above`
#    - Jeżeli jest mniejsza, to wypisz `Below`
# 3. Wymagania niefunkcjonalne:
#    - Użytkownik zawsze wpisze tylko jedną cyfrę
#    - Użytkownik nie wpisze żadnych nieprawidłowych znaków lub dłuższych liczb
#    - `Mock` zasymuluje wpisanie liczb przez użytkownika
#    - Skorzytaj z funkcji `input()` tak jak normalnie
# 4. Uruchom doctesty - wszystkie muszą się powieść

# %% Hints
# - `Stop` or `Ctrl+C` kills infinite loop

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

# Following two lines is needed for test automation
# In your code use `input()` function as normal
# `Mock` will simulate inputting numbers by a user
# So that, first number is `0`, second is `9`, and so on
from unittest.mock import Mock
input = Mock(side_effect=['0', '9', '1', '8', '2', '7', '3', '6', '4'])


HIDDEN = 4

# %% 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

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

# %% About
# - Name: While Break Grades
# - Difficulty: medium
# - Lines: 14
# - Minutes: 13

# %% English
# 1. Define `grades: list[float]`
# 2. Using `input()` ask user about grade, one at a time
# 3. User will type only valid `int` or `float`
# 4. To iterate use only `while` loop
# 5. If grade is in `GRADE_SCALE` - add it to `grades`
# 6. If grade is not in `GRADE_SCALE`, skip this iteration
# 7. If user pressed Enter key, end inserting data
# 8. Define `result: float` with arithmetic mean of `grades`
# 9. Test case when report list is empty
# 10. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `grades: list[float]`
# 2. Do iterowania użyj tylko pętli `while`
# 3. Używając `input()` poproś użytkownika o ocenę, jedną na raz
# 4. Użytkownik poda tylko poprawne `int` lub `float`
# 5. Jeżeli ocena jest w `GRADE_SCALE` - dodaj ją do `grades`
# 6. Jeżeli oceny nie ma w `GRADE_SCALE`, pomiń tą iterację
# 7. Jeżeli użytkownik wcisnął Enter, zakończ wprowadzanie danych
# 8. Zdefiniuj `result: float` ze średnią arytmetyczą `grades`
# 9. Przetestuj przypadek, gdy dzienniczek jest pusty
# 10. Uruchom doctesty - wszystkie muszą się powieść

# %% Hints
# - `Stop` or `Ctrl+C` kills infinite loop
# - If user hit enter key, without typing a number
# - Variable `grade` will be equal to `''` (empty string)
# - Keyword `break` will exit the loop
# - `mean = sum(...) / len(...)`

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

>>> from statistics import mean

>>> type(grades)
<class 'list'>
>>> type(result)
<class 'float'>

>>> assert all(type(x) is float for x in grades)

>>> mean(grades) == result
True

>>> result
3.5
"""

# Simulate user input (for test automation)
from unittest.mock import Mock
input = Mock(side_effect=['2', '2.5', '3', '3.5', '4', '5', '6', ''])


GRADE_SCALE = (2.0, 3.0, 3.5, 4.0, 4.5, 5.0)

# All user grades
# type: list[float]
grades = ...

# Arithmetic mean of grades
# type: float
result = ...