Скачать или смотреть #6 Learn Python code

Slide 1

So, What Does This Python Program Do?

def myst(s):
n = len(s)
match n:
case 0 | 1:
return True
case _ if s[0] == s[n-1]:
return myst(s[1:n-1])
case _:
return False

:hand: Pause the Video, if You Need to.

#Python #Beginner #Algorithm


Slide 2

Here's an Example Usage:

^^^ myst("madam")
???

What Would be the Output?

Another Example:

^^^ myst('Taco Cat')
???

:hand: Again, Pause the Video Here,
If You Need to.


Slide 3

Let's Walk through the Code:

def myst(s):
n = len(s)
match n:
case 0 | 1:
return True
...

:small_orange_diamond: First,
Based on `len`, and Slicing,
The Argument `s` is a [Sequence,]
Like a [List] or [String.]
:small_orange_diamond: The `myst` Function Then
Returns a Boolean Value.
:small_orange_diamond: `myst` is [Recursively] Implemented.
:small_orange_diamond: The Second Statement in `myst` is
[A `match` Statement]


Slide 4

match n:
case 0 | 1:
return True
...
case _:
return False

Python's `match` Statement
Starts with the Keyword `match` Followed by an Expression, and
It Consists of `case` Clauses.
Each `case` Includes a ["Pattern".]
If the Match Expression Matches One of These Patterns, Then
Its [Code Block] is Executed, and
It Exits the `match` Statement.
The Pattern `_` is Special in That
[It Matches Any Expression.]{.persimmon-text}


Slide 5

A `case` Clause Can Include
An `if` ["Match Guard".]
A Pattern with a Match Guard
Can Match the Match Expression
Only if it First Satisfies
The Match Guard.

case _ if s[0] == s[n-1]:
return myst(s[1:n-1])

Now,
Although this `case`
Includes the Catch-All Pattern, `_`,
It Will Not Match the Expression `n`
Unless the Condition `s[0] == s[n-1]`
Is First Satisfied.


Slide 6

Now, If You Go through
The Entire `match` Statement,
From Top to Bottom,
[Then]
You Will Realize that
It is Checking
If the Given Sequence, `s`,
Is a ["Palindrome".]

If We Run the Example Code,

^^^ myst("madam")
True

^^^ myst('Taco Cat')
False


Slide 7

Practice Quiz:

[1] First, Make Sure that You Understand the Implementation of the `myst` Function.
[2] Implement [the `match` Statement] in `myst`
Using [an `if` Statement.]
[3] Implement a Function, `is_palindrome`, [Iteratively,]
e.g., without Using Recursion.


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