Some function need 'constant' values (ie. not designed to be redefined later) that are not to be parametrized. While default arguments are stored only once for each function, some are just not very meaningful to be put as parameters (ie. to be part of the signature). For (a not very useful) example: def foo(bar): my_map = {"rab": barType, "oof": fooType} return my_map.get(bar,d
某些函数需要“常量”值（即，未设计为稍后重新定义），这些值不会被参数化。 虽然默认参数对于每个函数只存储一次，但有些参数并不是很有意义（即成为签名的一部分）。 对于（不是很有用）的例子： def foo(bar): my_map = {"rab": barType, "oof": fooType} return my_map.get(bar,defaultType)() 它浪费了CPU时间和RAM空间来为每次调用重新定义这样一个常量。 其他一些方法是将这些常量存储为模块级全局变量或将该
class Example(object): def the_example(self): itsProblem = "problem" theExample = Example() print(theExample.itsProblem) How do I access a class's variable? I've tried adding this definition: def return_itsProblem(self): return itsProblem Yet, that fails also. The answer, in a few words In your example, itsProblem is a local variable. Your must use self to set an
class Example(object): def the_example(self): itsProblem = "problem" theExample = Example() print(theExample.itsProblem) 我如何访问一个类的变量？ 我试过添加这个定义： def return_itsProblem(self): return itsProblem 但是，这也失败了。 用几句话来回答 在你的例子中， itsProblem是一个局部变量。 你必须使用self来设置和获取实例变量。 你可以在__init__方法中设置它。 那么你的代码
This question already has an answer here: Meaning of @classmethod and @staticmethod for beginner? 12 answers You are using __init__ method as a class method. Using @classmethod for every method will result in a singleton, that's why the vars overwrite.
这个问题在这里已经有了答案： @classmethod和@staticmethod对初学者的意义？ 12个答案 您正在使用__init__方法作为class方法。 对每种方法使用@classmethod将导致一个单例，这就是为什么变量被覆盖。
This question already has an answer here: Meaning of @classmethod and @staticmethod for beginner? 12 answers What are Class methods in Python for? 15 answers If you see _randomize method, you are not using any instance variable (declared in init) in it but it is using a class var ie RANDOM_CHOICE = 'abcdefg' . import random class Randomize: RANDOM_CHOICE = 'abcdefg' def
这个问题在这里已经有了答案： @classmethod和@staticmethod对初学者的意义？ 12个答案 Python中的类方法是什么？ 15个答案 如果你看到_randomize方法，你没有使用任何实例变量（在init中声明），但它使用了一个类var即RANDOM_CHOICE = 'abcdefg' 。 import random class Randomize: RANDOM_CHOICE = 'abcdefg' def __init__(self, chars_num): self.chars_num = chars_num def _randomi
This question seems mind-boggling simple, yet I can't figure it out. I know you can check datatypes in python, but how can you set a conditional based on the datatype? For instance, if I have to write a code that sorts through a dictionary/list and adds up all the integers, how do I isolate the search to look for only integers? I guess a quick example would look something like this: y =
这个问题似乎令人难以置信，但我无法弄清楚。 我知道你可以在python中检查数据类型，但是如何根据数据类型设置一个条件？ 例如，如果我必须编写一个通过字典/列表进行排序并将所有整数相加的代码，那么如何将搜索分离为仅查找整数？ 我想一个简单的例子看起来像这样： y = [] for x in somelist: if type(x) == <type 'int'>: ### <--- psuedo-code line y.append(x) print sum(int(z) for z in y) 所以
A question of semantics, really. Up until recently, if I had to do any typechecking on a structure, I would use type(obj) is list et. al. However since joining SO I've noticed everyone (and I mean EVERYONE) uses isinstance(obj,list) instead. It seems they are synonymous, and timeit reveals almost IDENTICAL speed between them. def a(): return type(list()) is list def b(): return isinstan
一个语义问题，真的。 直到最近，如果我必须对结构进行任何type(obj) is list ，我会使用type(obj) is list et。 人。 然而，自从加入后，我注意到每个人（我的意思是每个人）都使用isinstance(obj,list) 。 看起来它们是同义词， timeit揭示了它们之间几乎相同的速度。 def a(): return type(list()) is list def b(): return isinstance(list(),list) from timeit import timeit timeit(a) # 0.5239454597495582 timeit(
I came across this problem when attempting to learn python. Consider the following function: def swap0(s1, s2): assert type(s1) == list and type(s2) == list tmp = s1[:] s1 = s2[:] s2 = tmp return s1 = [1] s2 = [2] swap0(s1, s2) print s1, s2 What will s1 and s2 print? After running the problem, I found that the print statement will print 1 2. It seems that the value of s1 and
试图学习python时遇到了这个问题。 考虑以下功能： def swap0(s1, s2): assert type(s1) == list and type(s2) == list tmp = s1[:] s1 = s2[:] s2 = tmp return s1 = [1] s2 = [2] swap0(s1, s2) print s1, s2 s1和s2会打印什么？ 运行问题后，我发现print语句会打印1 2个swap0 。似乎s1和s2的值不会从swap0函数改变。 我能想到的唯一解释是因为这条线。 tmp = s1[:] 由于s1 [：]是一个副本，因此s1的
A function should select rows in a table based on the row name (column 2 in this case). It should be able to take either a single name or a list of names as arguments and handle them correctly. This is what I have now, but ideally there wouldn't be this duplicated code and something like exceptions would be used intelligently to choose the right way to handle the input argument: def selec
函数应该根据行名选择表中的行（在这种情况下为第2列）。 它应该能够将单个名称或名称列表作为参数并正确处理它们。 这就是我现在所拥有的，但理想情况下不会有这个重复的代码，并且类似异常的东西将被智能地用来选择正确的方式来处理输入参数： def select_rows(to_select): # For a list for row in range(0, table.numRows()): if _table.item(row, 1).text() in to_select: table.selectRow(
How is possible in python to check (without checking individually every element if possible) if the elements of a list are of the same type? For example, I would like to have a function to check that every element of this list is integer (which is clearly false): x=[1, 2.5, 'a'] def checkIntegers(x): # return true if all elements are integers, false otherwise Try using all in conjunction
如果列表中的元素是相同类型的，python如何检查（如果可能，不单独检查每个元素）？ 例如，我想有一个函数来检查这个列表中的每个元素是整数（这显然是错误的）： x=[1, 2.5, 'a'] def checkIntegers(x): # return true if all elements are integers, false otherwise 尝试将all与isinstance结合使用： all(isinstance(x, int) for x in lst) 如果需要的话，您甚至可以使用isinstance检查多种类型： all(isinstance(
when my function f is called with a variable I want to check if var is a pandas dataframe: def f(var): if var == pd.DataFrame(): print "do stuff" I guess the solution might be quite simple but even with def f(var): if var.values != None: print "do stuff" I can't get it to work like expected. isinstance, nothing else. PEP8 says explicitly that isinstance is the preferred way to
当我的函数f被一个变量调用时，我想检查var是否是一个熊猫数据框： def f(var): if var == pd.DataFrame(): print "do stuff" 我想这个解决方案可能很简单，但即使如此 def f(var): if var.values != None: print "do stuff" 我无法像预期那样工作。 isinstance，没有别的。 PEP8明确表示isinstance是检查类型的首选方法 Yes: if isinstance(obj, int): No: if type(obj) is type(1): 甚至不要考虑 if obj.__