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Python reference note7 - compound statements

15 Jul 2015

for statement: for i in expression_list , the expression list is evaluated once, it should yield an iterable object.
in for statements, a break statement executed in the first suite terminates the loop without execting the else clauses's suite. a continue statement executed in the first suite skips the rest of the suite and continues with the next item, or with the else clause if there is no next item .
if two nested handlers exist for the same exception, and the exception occurs in the try clause of the inner handler, the outer handler will not handle the exception.
in try...else...finally... statements, the optional else clause is executed if and when control flows off the end of the try clause. exceptions in the else clause are not handled by the preceding except clauses.
if finally is present, it specifies a 'cleanup' handler. the try clause is executed, including any except and clauses. if an exception occurs in any of the clauses and is not handled, the excetion is temporarily saved. the finally clause is executed. if there is a saved exception, it is re-raised at the end of the finally clause. if the finally clause raises another exception, the saved exception is set as the context of the new exception. if the finally clause executes a return or break statement, the saved exception is discarded. the execption information is not availabel to the program during exection of the finally clause.
a function definition is an executeable statement. its execution binds the function name in the current local namespace to a function object. this function object contains a reference to the current global namespace as the global namespace to be used when the function is called. the function definition does not execute the function body, this gets executed only when the function is caled.
a function definition may be wrapped by one or more decorator expressions. decorator expressions are evaluated when the function is defined, in the scope that contains the function definition. the result must be a callable, which is invoked with the function object as the only argument. the returnd value is bound to the function name instead of the function object.
default parameter values are evaluated from left to right when the function definition is executed. this means that the expression is evaluated once, when the function is defined, and that the same 'pre-computed' value is used for each call.

class A():  def foo(self, lst = []):   lst.append('foo')   print(lst) a = A() a.foo() b = A() b.foo()

and the execution:

$ python fun.py  ['foo'] ['foo', 'foo']

variables defined in the definition are class attributes, they are shared by instances. instance attributes can be set in a method with self.name = value