Add Python-range-function-improved-for-Python2.md

Python-range-function-improved-for-Python2.md

@@ -0,0 +1,58 @@
+#  range function improved for Python2
+
+## This class allows you to have a similar performance to the python3 range in python2
+
+This class doesn't load all the elements of the range at the same time in a list in memory.
+
+```Python
+class range:
+    def __init__(self, start, end=None, step=None):
+        if step is not None and step > 0 and  end is not None and end <= start:
+            raise ValueError("The start value is lower than the end")
+        elif end is not None and end < start and step is not None and step > 0:
+            raise ValueError("The end value can't be higher than the start if the step is higher than 0")
+        elif step == 0:
+            raise ValueError("Step value can't be 0")
+        if end is None:
+            end = start
+            start = 0
+        if step is None:
+            step = 1
+        self.start = start - step
+        self.end = end
+        self.step = step
+        self.__actual = 0
+
+    def __getitem__(self, index):
+        if index < 0:
+            raise IndexError("Index value can't be lower than 0")
+        output = self.step * (index + 1) + self.start
+        if self.end > self.start and output >= self.end:
+            raise IndexError("Index out of range")
+        elif self.end < self.start and output <= self.end:
+            raise IndexError("Index out of range")
+        return output
+ 
+    def __next__(self):
+        val = None
+        try:
+            val = self.__getitem__(self.__actual)
+        except IndexError:
+            raise StopIteration()
+        self.__actual += 1
+        return val
+
+>>> from_0_to_9 = range(10)
+>>> print(list(from_0_to_9))
+[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+
+>>> from_1_to_minus9 = range(1, -10, -1)
+>>> for n in from_1_to_minus9:
+>>>     print(n)
+1
+0
+-1
+...
+-8
+-9
+```