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Added about for loops concept.

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BethanyG
2021-04-25 20:43:49 -07:00
committed by BethanyG
parent b621231a8c
commit 3fbf7377bb
1 changed files with 11 additions and 12 deletions
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concepts/loops/about.md
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@@ -26,6 +26,8 @@ eggs
>>> print(placeholders)
['green_spam', 'green_ham', 'green_eggs']
```
<br>
## `For`
@@ -53,9 +55,9 @@ Bongo starts with a B.
## Sequence Object `range()`
When there isn't a specific `iterable` given, the special [`range()`][range] sequence is used.
`range()` requires a number before which to `stop`, and can optionally take a `start` parameter.
If no `start` number is provided, the sequence will begin with 0.
When there isn't a specific `iterable` given, the special [`range()`][range] sequence is used.
`range()` requires a number before which to `stop`, and can optionally take a `start` parameter.
If no `start` number is provided, the sequence will begin with 0.
`range()` objects are `lazy` (_values are generated on request_), support all [common sequence operations][common sequence operations], and take up a fixed amount of memory, no matter how long the sequence.
Interestingly, `range()` [is not an iterator][range is not an iterator], and can be used many in non-looping contexts.
@@ -98,7 +100,7 @@ Interestingly, `range()` [is not an iterator][range is not an iterator], and can
## Values and Indexes with `enumerate()`
If both values and indexes are needed, the built-in [`enumerate()`][enumerate] will return an [`iterator`][iterator] over (`index`, `value`) pairs:
If both values and indexes are needed, the built-in [`enumerate()`][enumerate] will return an [`iterator`][iterator] over (`index`, `value`) pairs.
```python
@@ -117,9 +119,11 @@ Bird (at index 0) starts with a B.
Chicken (at index 1) doesn't start with a B.
Barrel (at index 2) starts with a B.
Apple (at index 3) doesn't start with a B.
```
The `enumerate()` function can also be set to *start* the index count at a different number.
# enumerate() can also be set to *start* the index count at a different number.
```python
# Here, the index count will start at 1.
>>> for position, word in enumerate(word_list, start=1):
@@ -209,26 +213,21 @@ Found the above b-words, out of 6 words in the word list.
... if word.startswith("S"):
... print("Found an S, stopping iteration.")
... break
...# This is not run, because break was triggered
... else:
...
# This is not run, because break was triggered
... print(f"Found the above b-words, out of {len(word_list)} words in the word list.")
...
Bird (at index 0) starts with a B.
Barrel (at index 2) starts with a B.
Bongo (at index 3) starts with a B.
Found an S, stopping iteration.
```
[next built-in]: https://docs.python.org/3/library/functions.html#next
[stopiteration]: https://docs.python.org/3/library/exceptions.html#StopIteration
[loop else]: https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops
[for statement]: https://docs.python.org/3/reference/compound_stmts.html#for
[range]: https://docs.python.org/3/library/stdtypes.html#range
[break statement]: https://docs.python.org/3/reference/simple_stmts.html#the-break-statement
[continue statement]: https://docs.python.org/3/reference/simple_stmts.html#the-continue-statement
[while statement]: https://docs.python.org/3/reference/compound_stmts.html#the-while-statement
[iterable]: https://docs.python.org/3/glossary.html#term-iterable
[truth value testing]: https://docs.python.org/3/library/stdtypes.html#truth-value-testing
[enumerate]: https://docs.python.org/3/library/functions.html#enumerate
[iterator]: https://docs.python.org/3/glossary.html#term-iterator