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--- lfa:2024:lab04 [2024/10/27 22:48]
cata_chiru [Subtitlu]
+++ lfa:2024:lab04 [2024/10/29 09:27] (current)
cata_chiru
@@ Line 50: / Line 50: @@
 Further, when writing python code for interviews, **the employers usually follow this aspect and grade you in consequence**.
 </note>
 ==== Your Task ====
@@ Line 64: / Line 62: @@
     crt_lst = list(set(lst))
     return sorted(crt_lst, key = lambda x: (len(x), x))
 # Global variable used to threshold the number of Star items
 INNER_STAR_NO_ITEMS = 3
 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 __len__(self) -> str:
+        '''Returns the length of the regular expression'''
+        pass
     def eval_gen(self):
         '''Prints the set of strings that the regular expression can generate'''
         pass
 # TODO 0: Implementati Clasa Void dupa blueprint-ul de mai sus
 class Void(Regex):
     '''Represents the empty regular expression'''
     # Va returna Void ca string
     def __str__(self) -> str:
         pass
     # Va genera un obiect din Python corespunzatoar clasei void
     def gen(self) -> [str]:
         pass
+    def __len__(self):
+        return 0
     def eval_gen(self):
         print("Void generates nothing")
 # TODO 1: Implementati Clasa Epsilon-String (Empty) dupa blueprint-ul de mai sus
 class Empty(Regex):
     '''Represents the empty string regular expression'''
     # Va returna Empty ca string
     def __str__(self) -> str:
         pass
     # Va returna o lista corespunzatoare a ce stringuri produce sirul vid
     def gen(self) -> [str]:
         pass
+    # Va returna lungimea corespunzatoare sirului vid
+    def __len__(self) -> int:
+        pass
     def eval_gen(self):
-        print("Empty string generates ''.")
+        print(f"Empty string has length {len(self)} generates ''.")
 # TODO 2: Implementati functionalitatile necesare pentru Clasa Symbol dupa blueprint-ul de mai sus
 class Symbol(Regex):
     '''Represents a symbol in the regular expression'''
     def __init__(self, char: str):
         self.char = char
     # TODO 2: Completati metodele __str__ si gen pentru clasa Symbol
     def __str__(self) -> str:
         pass
     def gen(self) -> [str]:
         pass
+    def __len__(self) -> int:
+        return 1
     def eval_gen(self):
         self.gen()
 	# Dorim sa pastram in atributul words al clasei curente stringurile generate cu gen(self)
-        return "Symbol {self.char} generates {self.words}"
+        return f"Symbol {self.char} has length {len(self)} generates {self.words}"
 # TODO 3: Implementati functionalitatile necesare pentru Clasa Union dupa blueprint-ul de mai sus
 class Union(Regex):
@@ Line 139: / Line 151: @@
     def __init__(self, *arg: [Regex]):
         self.components = arg
+    # TODO 3: Completati metodele __str__, gen, __len__ si eval_gen pentru clasa Union
-    # TODO 3: Completati metodele __str__, gen si eval_gen pentru clasa Union
+    # Hint: Look at the str.join method to create (expr1|expr2|...)
     def __str__(self) -> str:
+        pass
+    def gen(self) -> [str]:
+        pass
+    # We will consider the len of a Union as the max length of its components
+    def __len__(self) -> int:
         pass
-    def gen(self) -> [str]:
-	pass
     # Dupa modelul de la Symbol, vom dori ca urmatoarele eval sa implementeze
-    # return "Class {varianta toString() a clasei) generates {self.words}"
+    # return "Class {varianta toString() a clasei) has length {len(self)} and generates {self.words}"
     def eval_gen(self) -> str:
-	pass
+	    pass
 # TODO 4: Implementati functionalitatile necesare pentru Clasa Concat dupa blueprint-ul de mai sus
 class Concat(Regex):
     '''Represents the concatenation of two regular expressions'''
     def __init__(self, *arg : [Regex]):
         self.components = arg
-    # TODO 4: Completati metodele __str__, gen si eval_gen pentru clasa Concat
+    # TODO 4: Completati metodele __str__, gen, __len__ si eval_gen pentru clasa Concat
     def __str__(self) -> str:
+        pass
+    def gen(self) -> [str]:
+        pass
+    def __len__(self) -> int:
         pass
-    def gen(self) -> [str]:
-	pass
     def eval_gen(self) -> str:
-	pass
+	    pass
 # TODO 5: Implementati functionalitatile necesare pentru Clasa Star dupa blueprint-ul de mai sus
 class Star(Regex):
@@ Line 174: / Line 195: @@
     def __init__(self, regex: Regex):
         self.regex = regex
+        # To memorize the base words generated by the regex inside the star, we store them in a list
         self.base_words = [""]
-        self.base_gen()
         self.words = []
+    # TODO 5: Completati metodele __str__, gen, __len__, eval_gen pentru clasa Star
+    def __str__(self) -> str:
+        pass
+    def gen(self, no_items = 10) -> [str]:
+        pass
+    # To ease your implementation we will consider a big number e.g. 1000000 as Infinity
-    # TODO 5: Completati metodele __str__, gen, eval_gen pentru clasa Star
+    def __len__(self) -> int:
-    def __str__(self):
         pass
-    def base_gen(self):
+    def eval_gen(self, no_items = 10):
-        '''To memorize the base words generated by the regex inside the star, we store them in a list'''
-        if type(self.regex) == Star:
-	    # Implement Star.gen with a limiting threshold
 	    pass
-	# Implement Regex.gen for the rest
-	pass
-    def gen(self, no_items = 10):
-	pass
-    def eval_gen(self, no_items = 10):
-	pass
 if __name__ == "__main__":
-    # Example usage
     r1 = Symbol('a')
     r2 = Symbol('b')
     regex_union = Union(r1, r2)
     regex_union.eval_gen()
     e2 = Union(Symbol('a'),Symbol('b'), Symbol('c'))
     e4 = Concat(r1, e2)
     e4.eval_gen()
     e5 = Concat(e2, e2, r2)
     e5.eval_gen()
     star_ex = Star(r1)
     star_ex.eval_gen()
     regex_concat = Concat(regex_union, star_ex)
     regex_concat.eval_gen()
     last_expr = Concat(Star(Union(Symbol('a'), Symbol('b'))), Symbol('b'), Star(Symbol('c')))
     last_expr.eval_gen()
-    </code>
+</code>
-OBSERVATII DESPRE CUM ARATA ASTEA -> CONCAT STAR ETC
+The output should be similar to:
+<code>
+Union (a | b) has length 1 and generates ['a', 'b'].
+Concat (a(a | b | c)) has length 2 and generates ['aa', 'ab', 'ac'].
+Concat ((a | b | c)(a | b | c)b) has length 3 and generates ['aab', 'abb', 'acb', 'bab', 'bbb', 'bcb', 'cab', 'cbb', 'ccb'].
+Star (a*) has length 10000000 generates ['', 'a', 'aa', 'aaa', 'aaaa', 'aaaaa', 'aaaaaa', 'aaaaaaa', 'aaaaaaaa', 'aaaaaaaaa', 'aaaaaaaaaa', '...'].
+Concat ((a | b)(a*)) has length 10000001 and generates ['a', 'b', 'aa', 'ba', 'aaa', 'baa', 'aaaa', 'baaa', '...'].
+Concat (((a | b)*)b(c*)) has length 20000001 and generates ['b', 'ab', 'bb', 'bc', 'aab', 'abb', 'abc', 'bab', 'bbb', 'bbc', 'bcc', 'aaab', 'aabb', 'aabc', 'abab', 'abbb', 'abbc', 'abcc', 'baab', 'babb', 'babc', 'bbab', 'bbbb', 'bbbc', 'bbcc', 'bccc', '...'].
+</code>
+==== Implementation Details ====
+We have to take into account for the precedence rules and implement each possibility accordingly:
+For example, what is the outer class of a(a|b|c)?
+<hidden Answer>
+Concat
+</hidden>
+How can we write this Regex using our classes?
+<hidden Answer>
+Concat(Symbol('a'), Union(Symbol('a'), Symbol('b'), Symbol('c'))
+</hidden>
+<note>
+Note that we have used the following code structures that takes a variable number of parameters as inputs for Concat and Union constructors:
+<code python>
+    def __init__(self, *arg : [Regex]):
+        self.components = arg
+</code>
+This design choice was meant to ease your work when representing more complex regexes. The alternative would be to use binary operations and fuse the ones identical together: (a|b|c) = Concat(Symbol('a'), Concat(Symbol('b'), Symbol('c')) = (a|(b|c))
+</note>
+What should it generate?
+<hidden Answer>
+[aa, ab, ac]
+</hidden>
+Therefore, we should analyse each possibility and think for each class if having other types of regular expressions inside affects the way in which the regex generates further and adapt our code to suit those class-recursions.
-EXEMPLU DE OUTPUT PENTRU MAIN
+We should develop this process from simple examples to more complex ones: Symbol, Concat(Symbol, Symbol), Union(Symbol, Symbol), Concat(Symbol, Union), Concat(Union, Union)...
-DE SCRIS DESPRE CUM DACA PREFERA ALTFEL SA IMPLEMENTEZE CHAR, LEGATURA CU UNION SI CONCAT ( DE CE E CHAR LISTA), A*, SI NR DE PARAMETRII IN CONCATENARI/UNION POT FACE CUM VOR EI.
+<note>
+If there are design choices that do not suit you in this laboratory, please feel free to adapt your implementation accordingly, as far as you keep the same classes and the main functionalities for ''%%__str__%%'', ''gen'' and ''eval_gen''.
+</note>