Hello, all.
Already some programs , I tried to add a little only , the function .
If you are interested , please try .
For those of the original author , thank you .
SimpleRSSReader
https://gist.github.com/beer2011/fcc4aaeec2a0f489b8fa
@beer2011 , thanks for sharing. Nice to read through the code for ideas. One thing I spotted, that appears it's a potential problem.
feeds=[]
class FeedListController(object):
def __init__(self, feeds=[]):
self.feeds = feeds
self.table = None
From what I have been reading a few days ago, dynamic objects should not be in the param list as there are only ever evaluated once. Can produce some strange bugs. Maybe I am wrong, maybe only a problem for functions.
From what I remember they say better to do feeds = None
The problem and a potential solution:
def default_args_broken(my_list=[]):
my_list.append(len(my_list))
print(my_list)
def default_args_working(my_list=None):
my_list = my_list or []
my_list.append(len(my_list))
print(my_list)
default_args_broken() # [0]
default_args_broken() # [0, 1]
default_args_broken() # [0, 1, 2]
default_args_working() # [0]
default_args_working() # [0]
default_args_working() # [0]
@ccc
my_list or [] can have unintended side effects too because an empty list is evaluated as False. Consider this:
def append_something(my_list=None):
my_list = my_list or []
my_list.append(len(my_list))
foo = []
append_something(foo)
print foo # => [] -- huh?
bar = [0]
append_something(bar)
print bar # => [0, 1]
(Granted, the example is a bit contrived.)
And that is why you should write the None check using ternary if-else instead of or:
my_list = [] if my_list is None else my_list
hmm, seem to recognize this ;)
The reply to everyone who, thank you.
In fact, I, programming is amateur.
(For even English, but it is the same.sorry. ^^;; )
And to understand what has been taught, it is likely to take some time.
Again, thank you.
@beer2011 , understand. I am also learning. Still brought up a good discussion. I hadn't been aware of this proble. A tricky one.