ch07

ch07/context/decimal.prec.py

@@ -0,0 +1,46 @@
+# context/decimal.prec.py
+from decimal import Context, Decimal, getcontext, setcontext
+
+one = Decimal("1")
+three = Decimal("3")
+
+orig_ctx = getcontext()
+ctx = Context(prec=5)
+setcontext(ctx)
+print(ctx)
+print(one / three)
+setcontext(orig_ctx)
+print(one / three)
+
+
+"""
+$ python context/decimal.prec.py
+Context(prec=5, rounding=ROUND_HALF_EVEN, Emin=-999999,
+Emax=999999, capitals=1, clamp=0, flags=[],
+traps=[InvalidOperation, DivisionByZero, Overflow])
+0.33333
+0.3333333333333333333333333333
+"""
+
+
+orig_ctx = getcontext()
+ctx = Context(prec=5)
+setcontext(ctx)
+try:
+    print(ctx)
+    print(one / three)
+finally:
+    setcontext(orig_ctx)
+print(one / three)
+
+
+from decimal import localcontext
+
+with localcontext(Context(prec=5)) as ctx:
+    print(ctx)
+    print(one / three)
+print(one / three)
+
+
+with localcontext(Context(prec=5)), open("out.txt", "w") as out_f:
+    out_f.write(f"{one} / {three} = {one / three}\n")

ch07/context/generator.py

@@ -0,0 +1,38 @@
+# context/generator.py
+from contextlib import contextmanager
+
+@contextmanager
+def my_context_manager():
+    print("Entering 'with' context")
+    val = object()
+    print(id(val))
+    try:
+        yield val
+    except Exception as e:
+        print(f"{type(e)=} {e=} {e.__traceback__=}")
+    finally:
+        print("Exiting 'with' context")
+
+
+print("About to enter 'with' context")
+with my_context_manager() as val:
+    print("Inside 'with' context")
+    print(id(val))
+    raise Exception("Exception inside 'with' context")
+    print("This line will never be reached")
+
+print("After 'with' context")
+
+
+"""
+$ python context/generator.py
+About to enter 'with' context
+Entering 'with' context
+139768531985040
+Inside 'with' context
+139768531985040
+type(e)=<class 'Exception'> e=Exception("Exception inside 'with'
+ context") e.__traceback__=<traceback object at 0x7f1e65a42800>
+Exiting 'with' context
+After 'with' context
+"""

ch07/context/manager.class.py

@@ -0,0 +1,40 @@
+# context/manager.class.py
+class MyContextManager:
+    def __init__(self):
+        print("MyContextManager init", id(self))
+
+    def __enter__(self):
+        print("Entering 'with' context")
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        print(f"{exc_type=} {exc_val=} {exc_tb=}")
+        print("Exiting 'with' context")
+        return True
+
+
+ctx_mgr = MyContextManager()
+
+print("About to enter 'with' context")
+
+with ctx_mgr as mgr:
+    print("Inside 'with' context")
+    print(id(mgr))
+    raise Exception("Exception inside 'with' context")
+    print("This line will never be reached")
+
+print("After 'with' context")
+
+
+"""
+$ python context/manager.class.py
+MyContextManager init 140340228792272
+About to enter 'with' context
+Entering 'with' context
+Inside 'with' context
+140340228792272
+exc_type=<class 'Exception'> exc_val=Exception("Exception inside
+ 'with' context") exc_tb=<traceback object at 0x7fa3817c5340>
+Exiting 'with' context
+After 'with' context
+"""