iterable-unpacking

问题 Assume line is: "Chicago Sun 01:52" . What does *a, b, c = line.split() do? In particular, what is the significance of the asterisk? Edit: Upon testing it, it seems like "Chicago" , "Sun" and "01:52" are all stored in a , b and c . The asterisk seems to lead to "Chicago" being stored in a as the first element of a list. So, we have a = ["Chicago"] , b = "Sun" and c = "01:52" . Could anyone point to material on the functionality of the asterisk operator in this situation? 回答1: Splitting that

问题 I've often been frustrated by the lack of flexibility in Python's iterable unpacking. Take the following example: a, b = range(2) Works fine. a contains 0 and b contains 1 , just as expected. Now let's try this: a, b = range(1) Now, we get a ValueError : ValueError: not enough values to unpack (expected 2, got 1) Not ideal, when the desired result was 0 in a , and None in b . There are a number of hacks to get around this. The most elegant I've seen is this: a, *b = function_with_variable

问题 This question already has answers here : How do I reliably split a string in Python, when it may not contain the pattern, or all n elements? (5 answers) Closed 2 years ago . I've often been frustrated by the lack of flexibility in Python's iterable unpacking. Take the following example: a, b = "This is a string".split(" ", 1) Works fine. a contains "This" and b contains "is a string" , just as expected. Now let's try this: a, b = "Thisisastring".split(" ", 1) Now, we get a ValueError :

问题 This question already has answers here : How do I reliably split a string in Python, when it may not contain the pattern, or all n elements? (5 answers) Closed 2 years ago . I've often been frustrated by the lack of flexibility in Python's iterable unpacking. Take the following example: a, b = "This is a string".split(" ", 1) Works fine. a contains "This" and b contains "is a string" , just as expected. Now let's try this: a, b = "Thisisastring".split(" ", 1) Now, we get a ValueError :

问题 What I came up with is: keys, values = zip(*[(key, value) for (key, value) in my_dict.iteritems()]) But I am not satisfied. What do the pythonistas say? 回答1: What about using my_dict.keys() and my_dict.values()? keys, values = my_dict.keys(), my_dict.values() 回答2: keys, values = zip(*d.items()) 来源： https://stackoverflow.com/questions/6612769/is-there-a-more-elegant-way-for-unpacking-keys-and-values-of-a-dictionary-into-t

问题 I am new to python programming and need your help for the following: I want to return two lists from a function in python. How can i do that. And how to read them in the main program. Examples and illustrations would be very helpful. Thanks in advance. 回答1: You can return a tuple of lists, an use sequence unpacking to assign them to two different names when calling the function: def f(): return [1, 2, 3], ["a", "b", "c"] list1, list2 = f() 回答2: You can return as many value as you want by

问题 I'm playing now with Python 3.5 interpreter and found very interesting behavior: >>> (1,2,3,"a",*("oi", "oi")*3) (1, 2, 3, 'a', 'oi', 'oi', 'oi', 'oi', 'oi', 'oi') >>> [1,2,3,"a",*range(10)] [1, 2, 3, 'a', 0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> ('aw','aw',*range(10),*(x**2 for x in range(10))) ('aw', 'aw', 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 4, 9, 16, 25, 36, 49, 64, 81) >>> {"trali":"vali", **dict(q=1,p=2)} {'q': 1, 'p': 2, 'trali': 'vali'} >>> {"a",1,11,*range(5)} {0, 1, 2, 3, 4, 11, 'a'} I have

问题 This question already has answers here : What do *args and **kwargs mean? [duplicate] (5 answers) Closed 5 years ago . As mentioned in PythonCookbook, * can be added before a tuple, and what does * mean here? Chapter 1.18. Mapping Names to Sequence Elements: from collections import namedtuple Stock = namedtuple('Stock', ['name', 'shares', 'price']) s = Stock(*rec) # here rec is an ordinary tuple, for example: rec = ('ACME', 100, 123.45) In the same section, **dict presents: from collections

问题 Just came across this little bit of weirdness in Python and thought I'd document it write it as a question here in case anyone else is trying to find an answer with the same fruitless search terms I was Looks like tuple unpacking makes it so you can't return a tuple of length 1 if you're expecting to iterate over the return value. Although it seems that looks are deceiving. See the answers. >>> def returns_list_of_one(a): ... return [a] ... >>> def returns_tuple_of_one(a): ... return (a) ...

问题 This came up in a recent PyCon talk. The statement [] = [] does nothing meaningful, but it does not throw an exception either. I have the feeling this must be due to unpacking rules. You can do tuple unpacking with lists too, e.g., [a, b] = [1, 2] does what you would expect. As logical consequence, this also should work, when the number of elements to unpack is 0, which would explain why assigning to an empty list is valid. This theory is further supported by what happens when you try to