Add missing file

Author: Raymi306

app/pages/error_handling.py

@@ -0,0 +1,244 @@
+"""25_error_handling.md"""
+# pylint: disable=invalid-name
+# pylint: disable=bare-except
+# pylint: disable=unused-variable
+# pylint: disable=import-outside-toplevel
+# pylint: disable=disallowed-name
+
+
+def delta_original():
+    """
+    >>> delta = delta_original()
+    >>> delta(1)
+    1.0
+    >>> delta(2)
+    0.5
+    >>> delta(-2)
+    0.5
+    >>> delta(3.14)
+    0.3184713375796178
+    >>> delta(0)
+    Traceback (most recent call last):
+        ...
+    ZeroDivisionError: division by zero
+    >>> delta('foo')
+    Traceback (most recent call last):
+        ...
+    TypeError: unsupported operand type(s) for /: 'int' and 'str'
+    """
+    # START
+    def delta(x):
+        return abs(1 / x)
+    # END
+    return delta
+
+
+def divide_by_zero_guard():
+    """
+    >>> delta = divide_by_zero_guard()
+    >>> delta(0)
+    >>> delta(2)
+    0.5
+    >>> delta(-2)
+    0.5
+    """
+    # START
+    def delta(x):
+        if x == 0:
+            return None
+        return abs(1 / x)
+    # END
+    return delta
+
+
+def more_guards():
+    """
+    >>> delta = more_guards()
+    >>> delta(0)
+    >>> delta('foo')
+    >>> delta(2)
+    0.5
+    >>> delta(-2)
+    0.5
+    """
+    # START
+    def delta(x):
+        if x == 0 or not isinstance(x, (float, int)):
+            return None
+        return abs(1 / x)
+    # END
+    return delta
+
+
+def bare_except():
+    """
+    >>> bare_except()
+    That didn't work, let's carry on and try something else
+    """
+    def delta(x):
+        return abs(1 / x)
+    # START
+    try:
+        result = delta(0)
+    except:
+        print("That didn't work, let's carry on and try something else")
+    # END
+
+
+def nonbare_excepts():
+    """
+    >>> nonbare_excepts()
+    You tried to divide by zero!
+    Whoops!
+    """
+    def delta(x):
+        return abs(1 / x)
+    # START
+    try:
+        result = delta(0)
+    except ZeroDivisionError:
+        print("You tried to divide by zero!")
+    except TypeError:
+        print("You tried dividing something that is not divisible!")
+
+    # OR
+
+    try:
+        result = delta(0)
+    except (ZeroDivisionError, TypeError):
+        print("Whoops!")
+    # END
+
+
+def control_flow_else():
+    """
+    >>> control_flow_else()
+    Fail
+    """
+    def delta(x):
+        return abs(1 / x)
+    # START
+    try:
+        n = delta(0)
+    except:
+        print("Fail")
+    else:
+        print("Success")
+    # END
+
+
+def control_flow_finally():
+    """
+    >>> import random
+    >>> random.seed(4)
+    >>> control_flow_finally()
+    I only print when no error occurs
+    I will print every time
+    >>> control_flow_finally()
+    I only print when an error occurs
+    I will print every time
+    """
+    import random
+
+    def fail_maybe():
+        num = random.randint(0, 1)
+        if num == 1:
+            raise RuntimeError()
+
+    try:
+        fail_maybe()
+    except RuntimeError:
+        print("I only print when an error occurs")
+    else:
+        print("I only print when no error occurs")
+    finally:
+        print("I will print every time")
+
+
+# pylint: disable=unnecessary-lambda-assignment
+def overly_broad_is_bad():
+    """
+    >>> overly_broad_is_bad()
+    About to do task 4
+    (2, 0)
+    """
+    task_1 = task_2 = task_3 = lambda: 0
+    task_4 = task_5 = task_6 = cleanup = lambda: 0
+
+    # START
+    try:
+        task_1()
+        task_2()
+        task_3()
+        print("About to do task 4")
+        task_4()
+        foo = 2 + task_5()
+        cleanup()
+        return foo, task_6()
+    except:
+        print("Something went wrong!")
+        return None
+    # END
+
+
+def less_broad():
+    """
+    >>> less_broad()
+    About to do task 4
+    (2, 0)
+    """
+    task_1 = task_2 = task_3 = lambda: 0
+    task_4 = task_5 = task_6 = cleanup = lambda: 0
+    class TaskError(Exception):
+        """pass"""
+
+    # START
+    task_1()
+    task_2()
+
+    try:
+        task_3()
+    except TaskError as e:
+        print(f"Task 3 failed! {e}")
+        return None
+    else:
+        print("About to do task 4")
+        task_4()
+        foo = 2 + task_5()
+        return foo, task_6()
+    finally:
+        cleanup()
+    # END
+# pylint: enable=unnecessary-lambda-assignment
+
+
+def raise_your_own_1():
+    """
+    >>> raise_your_own_1()
+    """
+    def func():
+        raise RuntimeError("Optional information goes here")
+
+
+def raise_your_own_2():
+    """
+    >>> raise_your_own_2()
+    """
+    def func(num):
+        try:
+            return 2 / num
+        except ZeroDivisionError as e:
+            raise RuntimeError from e
+
+
+# pylint: disable=missing-class-docstring
+def create_your_own():
+    """
+    >>> create_your_own()
+    """
+    class MyException(Exception):
+        """Raised when the bad thing happens"""
+
+    class MyExceptionChild(MyException):
+        pass
+# pylint: enable=missing-class-docstring