✎ lfa:2024:lab04 [books]

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====== 4. Regex Representation in Python ======

In this laboratory we will be using **Python3** classes to introduce a possible representation of regular expressions inside code and ways to work with those Regexes.

We will start with a base ''class Regex'' that will function as an interface for future descendents:

<code python>
class Regex:
    '''Base class for Regex ADT'''

    def __str__(self) -> str:
        '''Returns the string representation of the regular expression'''
        pass

    def gen(self) -> [str]:
        '''Return a representative set of strings that the regular expression can generate'''
        pass

    def eval_gen(self):
        '''Prints the set of strings that the regular expression can generate'''
        pass
</code>

We remark the following aspects:

<note>
There is no ''%%__init__(self)%%'' blueprint, implying that descendants of ''Regex'' could be instantiated with ''Descendent()'' if we do not specifically overwrite this default functionality.

As we have mentioned in the [second laboratory]("https://ocw.cs.pub.ro/ppcarte/doku.php?id=lfa:2024:lab02") the corespondences with ''Java'' are:
  * ''self'' $ \rightarrow $ ''this''
  * ''%%__init__%%'' $ \rightarrow $ Class Constructor
  * ''%%__str__(self)%%'' $ \rightarrow $ ''toString()''
  

</note>

<note>
We have structures of type ''%%'''comment'''%%''. This is the preferred way of writing documentation for classes and functions in Python, as the structure produces a help dialogue box when hovering over functionalities with this type of comments.
</note>

<note>
We have interfaced the functionalities for the methods: ''%%__str__(self) -> str%%'', ''%%gen(self) -> [str]%%'', ''%%eval_gen(self)%%''.

By using the keyword ''pass'' we can create empty function/class definitions, otherwise the Python3 interpreter would throw an error for empty structures.
</note>

<note>
Although Python is dynamically typed, we still encourage you to write the types for parameters and outputs explicitly, as they **contribute to documenting the code**. 

Further, when writing python code for interviews, **the employers usually follow this aspect and grade you in consequence**.
</note>



==== Subtitlu ====

abc

<note>
Cum arata cod python

<code python>
def main():
    ...  # your code here
    
if __name__ == "__main__":
    main()
</code>

</note>