Add copy or no copy video

Author: jamesmurphy-mc

README.md

@@ -12,6 +12,7 @@ James and his team are available for consulting, contracting, code reviews, and
 
 | N | Code | Video | 
 | -- | --- |--- |
+| 114 | [src](videos/114_copy_or_no_copy) | [Python Iterators! COPY or NO COPY?](https://youtu.be/hVFKy9Gw95c) |
 | 113 | [src](videos/113_getting_rid_of_recursion) | [Getting around the recursion limit](https://youtu.be/1dUpHL5Yg8E) |
 | 112 | [src](videos/112_python_name_mangling) | [Every Python dev falls for this (name mangling)](https://youtu.be/0hrEaA3N3lk) |
 | 111 | [src](videos/111_python_closures) | [Functions within functions, closures, and variable scopes in Python](https://youtu.be/jXugs4B3lwU) |

videos/114_copy_or_no_copy/copy_or_no_copy.py

@@ -0,0 +1,142 @@
+import collections.abc
+import typing
+
+
+def list_example():
+    l = [1, 2, 3, 4]
+
+    for x in reversed(l):
+        print(x)
+
+
+class MyContainer:
+    def __init__(self, l):
+        self.l = l
+
+    def __getitem__(self, item):
+        return self.l[item]
+
+    def __len__(self):
+        return len(self.l)
+
+    def __iter__(self):
+        return iter(self.l)
+
+
+def custom_container_example():
+    l = [1, 2, 3, 4]
+    container = MyContainer(l)
+    print(f"{list(container)=}")
+    print(reversed(container))
+    # print(reversed(reversed(l))) # ERROR
+
+    it = reversed(l)
+    print(list(it))
+    print(list(it))
+
+
+class reversed:
+    def __init__(self, seq):
+        self.seq = seq
+        self.n = len(seq) - 1
+        if not hasattr(seq, '__getitem__'):
+            raise TypeError("not reversible")
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):  # called by next()
+        if self.n == -1:
+            raise StopIteration
+        n = self.n
+        self.n = n - 1
+        return self.seq[n]
+
+
+def reversed(seq):
+    n = len(seq) - 1
+    if not hasattr(seq, '__getitem__'):
+        raise TypeError("not reversible")
+    while n != -1:
+        yield seq[n]
+        n -= 1
+
+
+def copy_or_no_copy():
+    l = [("a", 1), ("b", 2), ("c", 3)]
+    d = dict(l)
+
+    makes_a_copy = [
+        dict(l),
+        frozenset(l),
+        list(l),
+        set(l),
+        sorted(l),
+        tuple(l),
+        l[::-1],  # or any slice
+        [x for x in l],
+    ]
+    for x in makes_a_copy:
+        print(x)
+
+    doesnt_make_a_copy = [
+        enumerate(l),
+        filter(None, l),
+        iter(l),
+        map(lambda x: x, l),
+        reversed(l),
+        zip(l, l),
+        d.keys(),
+        d.values(),
+        d.items(),
+        (x for x in l),
+    ]
+    for x in doesnt_make_a_copy:
+        print(x)
+
+
+def numpy_example():
+    import numpy as np
+
+    arr = np.array([1, 2, 3])
+    rev = arr[::-1]
+
+    print(arr)
+    print(rev)
+
+    print(arr.data)
+    print(rev.data)
+
+    print(arr.strides)
+    print(rev.strides)
+
+
+def sometimes_you_want_a_copy_example():
+    d = {"a": 1, "b": 2, "c": 3}
+
+    for char, val in list(d.items()):
+        d[char.upper()] = val
+
+    print(d)
+
+
+def iterable_vs_Iterable():
+    container = MyContainer([1, 2, 3])
+    print(isinstance(container, typing.Iterable))
+    print(isinstance(container, collections.abc.Iterable))
+
+    print(iter(container))
+    # print(container.__iter__)
+
+
+def main():
+    list_example()
+    custom_container_example()
+    copy_or_no_copy()
+    numpy_example()
+    sometimes_you_want_a_copy_example()
+    iterable_vs_Iterable()
+
+
+if __name__ == '__main__':
+    main()