277 lines
4.5 KiB
Markdown
277 lines
4.5 KiB
Markdown
# Flow Control for-loop
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{:.no_toc}
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<nav markdown="1" class="toc-class">
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* TOC
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{:toc}
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</nav>
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## The goal
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For what reason...
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Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
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**Logic blocks need to be indented. Preferable with 4 spaces!**
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## [The for statement](https://docs.python.org/3/reference/compound_stmts.html#the-for-statement)
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> The for statement is used to iterate over the elements of a sequence (such as a string, tuple or list) or other iterable object
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### With range()
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```python
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for i in range(0, 3):
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print(i)
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```
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Output:
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```python
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0
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1
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2
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```
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### [range()](https://docs.python.org/3/library/stdtypes.html#ranges)
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```python
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class range(stop)
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class range(start, stop[, step])
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```
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### With a list
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```python
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for i in [0, "A", 7, "nom num"]:
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print(i)
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```
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Output:
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```python
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0
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A
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7
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nom num
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```
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## The full statement
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```python
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for_stmt ::= "for" target_list "in" starred_list ":" suite
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["else" ":" suite]
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```
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## for loop (the truth)
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{: .topic-optional}
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This is an optional topic!
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The for loop is not counting up itself. It uses the \_\_iter\_\_ & \_\_next\_\_ combo of a instance of a class or a generator via [yield](https://docs.python.org/3/reference/simple_stmts.html#the-yield-statement).
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### Class
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```python
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class ClassIterExample:
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counter: int
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counter_max: int
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def __init__(self):
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self.counter = 8
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self.counter_max = 12
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def __iter__(self):
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return self
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def __next__(self):
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if self.counter < self.counter_max:
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self.counter += 1
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else:
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raise StopIteration
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important_result: int = self.counter**2
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return f"Element: {self.counter}", important_result
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test_instance = ClassIterExample()
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for i in test_instance:
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print(i)
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```
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Output:
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```python
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('Element: 9', 81)
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('Element: 10', 100)
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('Element: 11', 121)
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('Element: 12', 144)
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```
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### Generator yield
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```python
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from typing import Generator
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def do_more(min_value: int, max_value: int) -> Generator:
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for index in range(min_value, max_value):
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yield index**2
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for i in do_more(min_value=3, max_value=8):
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print(i)
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```
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Output:
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```python
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9
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16
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25
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36
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49
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```
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## for loop -- [enumerate](https://docs.python.org/3/library/functions.html#enumerate)
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```python
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enumerate(iterable, start=0)
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```
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If you need the index of the element then you can use enumerate:
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```python
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for i in enumerate(range(10, 13)):
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print(i)
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```
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Output:
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```python
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(0, 10)
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(1, 11)
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(2, 12)
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```
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{: .topic-optional}
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This is an optional topic!
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```python
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for i in enumerate(range(10, 13)):
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print(i)
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else:
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print("*")
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print(i)
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```
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Output:
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```python
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(0, 10)
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(1, 11)
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(2, 12)
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*
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(2, 12)
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```
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{: .topic-optional}
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This is an optional topic!
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```python
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class ClassIterExample:
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counter: int
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counter_max: int
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def __init__(self):
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self.counter = 8
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self.counter_max = 12
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def __iter__(self):
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return self
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def __next__(self):
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if self.counter < self.counter_max:
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self.counter += 1
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else:
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raise StopIteration
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important_result: int = self.counter**2
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return f"Element: {self.counter}", important_result
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test_instance = ClassIterExample()
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for i in enumerate(test_instance):
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print(i)
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```
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Output:
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```python
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(0, ('Element: 9', 81))
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(1, ('Element: 10', 100))
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(2, ('Element: 11', 121))
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(3, ('Element: 12', 144))
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```
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You see a tuple with the enumerate id as a first component and a second tuple as result from the iterator.
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## [break](https://docs.python.org/3/reference/simple_stmts.html#the-break-statement)
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> break may only occur syntactically nested in a for or while loop, but not nested in a function or class definition within that loop.
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> It terminates the nearest enclosing loop, skipping the optional else clause if the loop has one.
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> If a for loop is terminated by break, the loop control target keeps its current value.
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```python
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break_stmt ::= "break"
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```
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```python
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for i in range(0, 5):
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if i == 2:
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break
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print(i)
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```
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Output:
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```python
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0
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1
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```
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## [continue](https://docs.python.org/3/reference/simple_stmts.html#the-continue-statement)
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> continue may only occur syntactically nested in a for or while loop, but not nested in a function or class definition within that loop. It continues with the next cycle of the nearest enclosing loop.
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```python
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continue_stmt ::= "continue"
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```
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```python
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for i in range(0, 5):
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if i == 2:
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continue
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print(i)
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```
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Output:
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```python
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0
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1
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3
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4
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```
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