8.1. Loop While About¶
Iterate over sequences (iterables)
Repeat if until result is False
8.1.1. Syntax¶
Continue execution when argument is
TrueStops if argument is
False
Generic syntax:
while <condition>:
<do something>
Example:
>>>
... while True:
... pass
8.1.2. Getitem with Const¶
>>> data = ['a', 'b', 'c']
>>>
>>> print(data[0])
a
>>> print(data[1])
b
>>> print(data[2])
c
>>> print(data[3])
Traceback (most recent call last):
IndexError: list index out of range
8.1.3. Getitem with Variable¶
>>> data = ['a', 'b', 'c']
>>>
>>> i = 0 # i = 0
>>> print(data[i]) # data[0]
a
>>>
>>> i += 1 # i = 1
>>> print(data[i]) # data[1]
b
>>>
>>> i += 1 # i = 2
>>> print(data[i]) # data[2]
c
>>>
>>> i += 1 # i = 3
>>> print(data[i]) # data[3]
Traceback (most recent call last):
IndexError: list index out of range
8.1.4. Getitem with Boundary Checking¶
>>> data = ['a', 'b', 'c']
>>> len(data)
3
>>> data = ['a', 'b', 'c']
>>> i = 0
>>>
>>> if i < len(data):
... print(data[i]) # data[0]
... i += 1 # i = 1
a
>>>
>>> if i < len(data): # True
... print(data[i]) # data[1]
... i += 1 # i = 2
b
>>>
>>> if i < len(data): # True
... print(data[i]) # data[2]
... i += 1 # i = 3
c
>>>
>>> if i < len(data): # False
... print(data[i]) # will not execute
... i += 1 # will not execute
8.1.5. While Loop¶
>>> data = ['a', 'b', 'c']
>>> i = 0
>>>
>>> while i < len(data):
... print(data[i])
... i += 1
a
b
c
8.1.6. Sequence Iteration¶
Better idea for this is to use for loop. for loop supports Iterators. len() must write all numbers to memory, to calculate its length:
>>> i = 0
>>> data = ['a', 'b', 'c']
>>>
>>> while i < 3:
... print(i, data[i])
... i += 1
0 a
1 b
2 c
>>> i = 0
>>> data = ['a', 'b', 'c']
>>> length = 3
>>>
>>> while i < length:
... print(i, data[i])
... i += 1
0 a
1 b
2 c
>>> i = 0
>>> data = ['a', 'b', 'c']
>>>
>>> while i < len(data):
... print(i, data[i])
... i += 1
0 a
1 b
2 c
8.1.7. Good Practices¶
The longer the loop scope, the longer the variable name should be
Avoid one letters if scope is longer than one line
Use
ifor loop counter (it is traditional name in almost all languages)
8.1.8. Assignments¶
"""
* Assignment: Loop While Range
* Required: yes
* Complexity: easy
* Lines of code: 5 lines
* Time: 3 min
English:
1. Generate `result: list[int]` with numbers from 0 to 5 (exclusive)
2. Do not use `range()`
3. Run doctests - all must succeed
Polish:
1. Wygeneruj `result: list[int]` z liczbami od 0 do 5 (rozłącznie)
2. Nie używaj `range()`
3. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> assert type(result) is list
>>> assert all(type(x) is int for x in result)
>>> result
[0, 1, 2, 3, 4]
"""
# List with numbers from 0 to 5 (exclusive)
# type: list[int]
result = ...
"""
* Assignment: Loop For Count
* Required: yes
* Complexity: easy
* Lines of code: 13 lines
* Time: 8 min
English:
1. Count occurrences of each color
2. Do not use `list.count()`
3. Run doctests - all must succeed
Polish:
1. Zlicz wystąpienia każdego z kolorów
2. Nie używaj `list.count()`
3. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> assert red is not Ellipsis, \
'Assign your result to variable `red`'
>>> assert green is not Ellipsis, \
'Assign your result to variable `green`'
>>> assert blue is not Ellipsis, \
'Assign your result to variable `blue`'
>>> assert type(red) is int, \
'Variable `red` has invalid type, should be list'
>>> assert type(green) is int, \
'Variable `green` has invalid type, should be list'
>>> assert type(blue) is int, \
'Variable `blue` has invalid type, should be list'
>>> red
3
>>> green
2
>>> blue
2
"""
DATA = ['red', 'green', 'blue', 'red', 'green', 'red', 'blue']
# Number of 'red' elements in DATA
# type: int
red = ...
# Number of 'green' elements in DATA
# type: int
green = ...
# Number of 'blue' elements in DATA
# type: int
blue = ...
"""
* Assignment: Loop While toFloat
* Required: yes
* Complexity: easy
* Lines of code: 5 lines
* Time: 5 min
English:
1. Create `result: list[float]`
2. Use `while` to iterate over `DATA`
3. Convert current elements of `DATA` to `float`
4. Converted value append to `result`
5. Run doctests - all must succeed
Polish:
1. Stwórz `result: list[float]`
2. Użyj `while` do iterowania po `DATA`
3. Przekonwertuj obecny element `DATA` do `float`
4. Przekonwertowaną wartość dodaj na koniec `result`
5. Uruchom doctesty - wszystkie muszą się powieść
Hints:
* `Stop` or `Ctrl+C` kills infinite loop
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> type(result)
<class 'list'>
>>> assert all(type(x) is float for x in result)
>>> result
[2.0, 3.0, 3.5, 4.0, 4.5, 5.0]
"""
DATA = (2, 3, 3.5, 4, 4.5, 5)
# Values from DATA converted to float
# type: list[float]
result = ...
"""
* Assignment: Loop While toStr
* Required: yes
* Complexity: easy
* Lines of code: 4 lines
* Time: 5 min
English:
1. Create `result: str`
2. Use `while` to iterate over `DATA`
3. Add current element of `DATA` to `result`
4. Do not use `str.join()`
5. Run doctests - all must succeed
Polish:
1. Stwórz `result: str`
2. Użyj `while` do iterowania po `DATA`
3. Dodaj obecny element z `DATA` do `result`
4. Nie używaj `str.join()`
5. Uruchom doctesty - wszystkie muszą się powieść
Hints:
* `Stop` or `Ctrl+C` kills infinite loop
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> type(result)
<class 'str'>
>>> result
'hello'
"""
DATA = ['h', 'e', 'l', 'l', 'o']
# Joined DATA values
# type: str
result = ...
"""
* Assignment: Loop While Translate
* Required: yes
* Complexity: medium
* Lines of code: 5 lines
* Time: 5 min
English:
1. Use `while` to iterate over `DATA`
2. If letter is in `PL` then use conversion value as letter
3. Add letter to `result`
4. Run doctests - all must succeed
Polish:
1. Użyj `while` do iteracji po `DATA`
2. Jeżeli litera jest w `PL` to użyj skonwertowanej wartości jako litera
3. Dodaj literę do `result`
4. Uruchom doctesty - wszystkie muszą się powieść
Hints:
* `Stop` or `Ctrl+C` kills infinite loop
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> type(result)
<class 'str'>
>>> result
'zazolc gesla jazn'
"""
PL = {'ą': 'a', 'ć': 'c', 'ę': 'e',
'ł': 'l', 'ń': 'n', 'ó': 'o',
'ś': 's', 'ż': 'z', 'ź': 'z'}
DATA = 'zażółć gęślą jaźń'
# DATA with substituted PL diacritic chars to ASCII letters
# type: str
result = ...