On Sun, Dec 27, 2015 at 3:11 PM, <jf...@ms4.hinet.net> wrote: > Last night I noticed that Python does not resolve name in "def" during > import, as C does in the compile/link stage, it was deferred until it was > referenced (i.e. codes was executed). That's OK for Anyway codes has to be > debugged sooner or later. I just have to get used to this style. > > But check these codes, it seems not. > ------- > x = 1 # a global variable > print(x) > > class Test: > x = 4 # a class attribute > print(x) > def func(self): > print(x) > > x1 = Test() > x1.x = 41 # a instance's attribute > x1.func() # it's 1 but 41 was expect:-( > -------- > > --Jach
When you import this module, it runs all top-level code. So the 'print' at the top will happen at import time. Among the top-level statements is a class definition. When that gets run (to construct the class itself - distinct from instantiating it, which happens further down), it builds a class by executing all the statements in it, in order. That results in that value of x being printed, and then defines a function. The function definition is being run at time of class construction, and it creates a new attribute on the Test class. At that time, the function body isn't actually executed (as you might expect). However, it's worth noting that the function does not inherit class scope. The unadorned name 'x' references the global. If you want to access class-scope names from inside methods, you need to say 'self.x', which also applies to instance attributes. That's what would do what you expect here. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
