isinstance

问题 Suppose I have a class FakePerson which imitates all the attributes and functionality of a base class RealPerson without extending it . In Python 3, is it possible to fake isinstance() in order to recognise FakePerson as a RealPerson object by only modifying the FakePerson class. For example: class RealPerson(): def __init__(self, age): self.age = age def are_you_real(self): return 'Yes, I can confirm I am a real person' def do_something(self): return 'I did something' # Complicated

问题 All I'm looking for is a list of possible values of classinfo since the documentation doesn't provide one and I can't seem to find one anywhere else online, let alone SO. 回答1: print([t for t in __builtins__.__dict__.values() if isinstance(t, type)]) Output (line-breaks inserted for readability): [ <class '_frozen_importlib.BuiltinImporter'>, <class 'bool'>, <class 'memoryview'>, <class 'bytearray'>, <class 'bytes'>, <class 'classmethod'>, <class 'complex'>, <class 'dict'>, <class 'enumerate'>

问题 How would I use a negative form of Python's isinstance()? Normally negation would work something like x != 1 if x not in y if not a I just haven't seen an example with isinstance(), so I'd like to know if there's a correct way to used negation with isinstance(). 回答1: Just use not . isinstance just returns a bool , which you can not like any other. 回答2: That would seem strange, but: if not isinstance(...): ... The isinstance function returns a boolean value. That means that you can negate it

问题 How would I use a negative form of Python's isinstance()? Normally negation would work something like x != 1 if x not in y if not a I just haven't seen an example with isinstance(), so I'd like to know if there's a correct way to used negation with isinstance(). 回答1: Just use not . isinstance just returns a bool , which you can not like any other. 回答2: That would seem strange, but: if not isinstance(...): ... The isinstance function returns a boolean value. That means that you can negate it

问题 I have a Python script that reads in a .csv file and stores each of the values into a list of lists: list[x][y]. I don't have any issues with this. list = [] i = 0 for row in reader: list.append([]) list[i].append(row[0]) ... i += 1 I want to check one of these fields to see if it's an number (integer). When I perform a print type(list[i][0]) it returns a <type 'str'> even though the value is say 100. The if statements below are in a for loop iterating through the lists so what I was thinking

问题 I have a variable which may or may not be a sympy class. I want to convert it to a float but I’m having trouble doing this in a general manner: $ python Python 2.7.3 (default, Dec 18 2014, 19:10:20) [GCC 4.6.3] on linux2 >>> import sympy >>> x = sympy.sqrt(2) >>> type(x) <class 'sympy.core.power.Pow'> >>> y = 1 + x >>> type(y) <class 'sympy.core.add.Add'> >>> z = 3 * x >>> type(z) <class 'sympy.core.mul.Mul'> >>> if isinstance(z, sympy.core): ... z = z.evalf(50) # 50 dp ... Traceback (most

问题 Below is sample code that subclasses datetime. Since pass is the only subclass body, method '__new__' of datetime is expected to be preserved. The following code has been tested on Python 3.4.2 on Mac OS 10.12.3 and Python 3.6.0 on Arch Linux. In both cases, same result. The question is, why is 'a' an instance of MyDatetime when 'b' is not an instance of MyDatetime when they differ only by argument tz? Thank you for your feedback. Now on with the example... #!/usr/bin/env python3 from

问题 I'm fairly new to C++, I've been mainly using python. I'm trying to check the type of variable of the value stored in the objects I'm working on. I remember that in Python there was a comand isinstance where I could use it as a condition to run certain commands, like if the next value is a string, do A, and if it's an int do B. Is there a way to quickly check what's the data type on a variable in C++? Example: In python I had an array with a math operation, each character in a field [3,"+",2]

问题 I'm looking at this piece of code written by someone else, and I'm wondering when it would evaluate to true. Basically, it is saying someType is an instance of someOtherType. Does it even make sense? So far, I've tried: derivedClass.GetType().IsInstanceOfType(typeof(BaseClass)) baseClass.GetType().IsInstanceOfType(typeof(DerivedClass)) myClass.GetType().IsInstanceOfType(typeof(MyClass)) And all of them evaluate to false. Any help is appreciated. 回答1: Each of those 3 lines will return true

问题 I am trying to check if an input is a word or a number. var = input("var: ") if isinstance(var, str): print "var = word" else: print "var = number" This is the code I came up with but sadly doesn't work; I'm new to python and programming in general so I don't know alot of commands, any suggestion would be appreciated ^^ 回答1: input() will take and evaluate your input before handing it over to you. That is, if the user enters exit() , your application will exit. This is undesirable from a