add a note about using __slots__

lupescudaniel · Jan 20, 2018 · 16b3fe2 · 16b3fe2
1 parent dcc23be
commit 16b3fe2
Showing 1 changed file with 64 additions and 0 deletions.
diff --git a/docs/notes/python-basic.rst b/docs/notes/python-basic.rst
@@ -1333,6 +1333,70 @@ Parsing csv string
     ['foo', 'bar', 'baz']
 
 
+Using ``__slots__`` to save memory
+-----------------------------------
+
+.. code-block:: python
+
+    #!/usr/bin/env python3
+
+    import resource
+    import platform
+    import functools
+
+
+    def profile_mem(func):
+        @functools.wraps(func)
+        def wrapper(*a, **k):
+            s = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+            ret = func(*a, **k)
+            e = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+
+            uname = platform.system()
+            if uname == "Linux":
+                print(f"mem usage: {e - s} kByte")
+            elif uname == "Darwin":
+                print(f"mem usage: {e - s} Byte")
+            else:
+                raise Exception("not support")
+            return ret
+        return wrapper
+
+
+    class S(object):
+        __slots__ = ['attr1', 'attr2', 'attr3']
+
+        def __init__(self):
+            self.attr1 = "Foo"
+            self.attr2 = "Bar"
+            self.attr3 = "Baz"
+
+
+    class D(object):
+
+        def __init__(self):
+            self.attr1 = "Foo"
+            self.attr2 = "Bar"
+            self.attr3 = "Baz"
+
+
+    @profile_mem
+    def alloc(cls):
+        _ = [cls() for _ in range(1000000)]
+
+
+    alloc(S)
+    alloc(D)
+
+output:
+
+.. code-block:: console
+
+    $ python3.6 s.py
+    mem usage: 70922240 Byte
+    mem usage: 100659200 Byte
+
+
 Using annotation to check type
 -------------------------------