34 lines
1.9 KiB
Markdown
34 lines
1.9 KiB
Markdown
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# Concepts of `reverse-string`
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## Example implementation:
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From the current [example.py](https://github.com/exercism/python/blob/master/exercises/reverse-string/example.py):
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```python
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def reverse(text: str = "") -> str:
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"""Reverse a given string"""
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return text[::-1]
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```
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## Concepts
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- [Function][function]: `def` to create a function in Python
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- [Immutability][immutability]: `text` str in Python is [immutable](https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str).
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In this exercise, you return a new string, the old string `text` is not changed.
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- [Return Value][return-value]: this function return a string by this line: `return text[::-1]`
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- [Slicing][slicing]: becase `str` in Python is a sequence type, [slicing](https://docs.python.org/3/reference/expressions.html#slicings) syntax can be used here. Specifically: for syntax `string[start:stop:stride]`:
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- `start`: 0-index of the start position, `start=0` by default (i.e., not specified) (start from the beginning)
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- `stop`: 0-index of the stop position, `stop=-1` by default (i.e., not specified) (stop at the end)
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- `stride`: number of skip step. For example,
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```python
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>>> string = 'ABCDEF'[::2]
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>>> print(string)
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'ACE'
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```
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- In this exercise, `stride = -1` means start from the end
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Together effectively, slicing of `[::-1]` gives the reversed string
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[Extra material for string slicing.](https://www.digitalocean.com/community/tutorials/how-to-index-and-slice-strings-in-python-3)
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- [Docstrings][docstrings]: used to document the function, normally situated right below `def func():`
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- [Type hinting][type-hinting]: In modern Python it's possibly to type hint annotations to parameters and variables, see [typing](https://docs.python.org/3/library/typing.html#module-typing). While not neccessary in Python such annotations can help your code be easier to read, understand, and check automatically using tools like `mypy`.
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