added string exercise

strings/string_manipulation/README.md

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+# Mit Zeichenketten arbeiten und manipulieren
+
+Diese Teilaufgaben sind teilweise sehr einfach zu implementieren und sollen veranschaulichen was man alles mit Strings machen kann. Hierbei könnt ihr euch es natürlich einfach machen und die Buildins von `str` verwenden oder die Funktionen komplett selber implementieren.
+

strings/string_manipulation/solution/strings.py

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+from dataclasses import dataclass, InitVar
+from typing import Iterator
+
+type Str = 'String' | str
+
+@dataclass
+class String:
+    _s: InitVar[str]
+    
+    def __post_init__(self, s: str) -> None:
+        self.__s = s
+        
+    def __str__(self) -> str:
+        return self.__s
+    
+    def __add__(self, other: Str) -> 'String':
+        return String(self.__s + str(other))
+            
+    def __iadd__(self, other: Str) -> 'String':
+        return self + other
+    
+    def __len__(self) -> int:
+        return len(self.__s)
+    
+    def __eq__(self, other: Str) -> bool:
+        return str(self) == str(other)
+            
+    def concat(self, other: Str) -> None:
+        self + other
+        
+    def contains(self, other: Str) -> bool:
+        s = str(other)
+        for c in str(self):
+            if len(s) <= 0:
+                break
+            elif c == s[0]:
+                s: str = s[1:]
+            else:
+                s = str(other)
+        return len(s) == 0
+    
+    def concat(self, other: Str) -> None:
+        self.__s += str(other)
+        
+    def substring(self, start: int, end: int) -> 'String':
+        substr: str = ""
+        for i, c in enumerate(self.__s):
+            if i >= start and i <= end:
+                substr += c
+        return substr
+    
+    def strip(self, chars: Str = ' ' + '\n' + '\t' + '\r') -> None:
+        i = 0
+        while i < len(self) and self.__s[i] in chars:
+            i += 1
+        j: int = len(self) - 1
+        while i <= j and self.__s[j] in chars:
+            j -= 1
+        self.__s: str = str(self)[i:j + 1]
+        
+    def replace(self, old: Str, new: Str, count = -1) -> None:
+        o = str(old)
+        n = str(new)
+        j = 0
+        while count > 0 or (count < 0 and j < len(self)):
+            i: int = j
+            while len(o) > 0 and j < len(self):
+                if o[0] == self.__s[j]:
+                    o: str = o[1:]
+                    j += 1
+                else:
+                    j += 1
+                    break
+            if len(o) <= 0:
+                self.__s = self.__s[:i] + n + self.__s[j:]
+                j += len(new) - len(old)
+                count -= 1
+            o = str(old)
+    
+    def add_prefix(self, prefix: Str) -> None:
+        self.__s = str(prefix) + self.__s
+        
+    def add_suffix(self, suffix: Str) -> None:
+        self.__s += str(suffix)
+        
+    def join[T](self, xs: Iterator[T]) -> 'String':
+        output = String("")
+        length: int = len(xs)
+        for i, e in enumerate(xs):
+            output += str(e)
+            if i < length - 1:
+                output += self
+        return output

strings/string_manipulation/solution/test_strings.py

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+from strings import String
+
+def test_eq_for_str():
+    test_str = String("this is a test string!")
+    assert test_str == "this is a test string!", "__eq__ wasn't implemented correctly for `String` and `str`"
+
+def test_strings_contains():
+    test_str = String("this is a test")
+    assert test_str.contains("this")
+    assert not test_str.contains("release")
+   
+def test_strings_concat():
+    test_str = String("")
+    test_str += "test succesful!"
+    assert test_str == "test succesful!"
+    test_str.concat(" Or is it?")
+    assert test_str == "test succesful! Or is it?"
+    
+def test_strings_strip():
+    test_str = String("           halo?      \n")
+    test_str.strip()
+    assert test_str == "halo?"
+    test_str = String("    \n       ")
+    test_str.strip()
+    assert test_str == ""
+   
+   
+def test_strings_replace():
+    test_str = String("har har har, try replacing thhis") 
+    test_str.replace('har ', 'ha')
+    assert test_str == "hahahar, try replacing thhis"
+    test_str.replace('r', '', 1)
+    assert test_str == "hahaha, try replacing thhis"
+    test_str.replace('hh', 'h')
+    assert test_str == "hahaha, try replacing this"
+    test_str.replace('try replacing this', "replaced")
+    assert test_str == "hahaha, replaced"
+    
+    
+def test_add_pre_suf():
+    test_str = String(" ")
+    test_str.add_suffix("suff")
+    assert test_str == " suff"
+    test_str.add_prefix("pref")
+    assert test_str == "pref suff"
+    
+def test_join():
+    assert String(", ").join([1, 2, 3, 4]) == "1, 2, 3, 4"
+    assert String(", ").join([]) == ""