Hướng dẫn dùng python string.contains python

str.find[str, beg=0 end=len[string]]

str1 = "Vi du \t ham find[] trong Python";
str2 = "find";
print [str1.find[str2]]
print [str1.find[str2, 10]]
print [str1.find[str2, 20]]

str.find[str, beg=0 end=len[string]]

str1 = "Vi du \t ham find[] trong Python";
str2 = "find";
print [str1.find[str2]]
print [str1.find[str2, 10]]
print [str1.find[str2, 20]]

Here is my code:

class a[object]:
    d='ddd'
    def __contains__[self]:
        if self.d:return True
b=a[]
print b.contains['d']  # error
print contains[b,'d']  # error

Chris Martin

29.6k8 gold badges74 silver badges131 bronze badges

asked Dec 27, 2009 at 1:49

Like all special methods [with "magic names" that begin and end in __], __contains__ is not meant to be called directly [except in very specific cases, such as up=calls to the superclass]: rather, such methods are called as part of the operation of built-ins and operators. In the case of __contains__, the operator in question is in -- the "containment check" operator.

With your class a as you present it [except for fixing your typo, and using True instead of true!-], and b as its instance, print 'x' in b will print True -- and so will any other containment check on b, since b always returns True [because self.d, a non-empty string, is true].

answered Dec 27, 2009 at 2:04

Alex MartelliAlex Martelli

821k163 gold badges1200 silver badges1377 bronze badges

to get your code to do something [although nothing useful]:

class a[object]:

    d = 'ddd'

    def __contains__[self, m]:
        if self.d: 
            return True

b = a[]

>>> 'd' in b
True

The docs.

Julius

7997 silver badges11 bronze badges

answered Dec 27, 2009 at 1:51

cobbalcobbal

68.9k19 gold badges142 silver badges155 bronze badges

__contains__ method defines how instances of class behave when they appear at right side of in and not in operator.

class Person[object]:
      def __init__[self,name,age]:
          self.name = name
          self.age = age
      def __contains__[self,param1]:
          return True if param1 in self.__dict__.keys[] else False

>>> p = Person['Robby Krieger',23]
>>> 'name' in p
True  

Azat Ibrakov

8,8669 gold badges37 silver badges45 bronze badges

answered Jan 1, 2013 at 9:33

vijay shankervijay shanker

2,3781 gold badge21 silver badges37 bronze badges

1

if self.d:return true

self.d is the string 'ddd'. Non-empty strings are always truthy: when you use if on 'ddd' it will always act as if you'd said if True:.

I think what you probably meant is:

def __contains__[self, item]:
    return item in self.d

in is the operator that calls the __contains__ method behind the scenes.

answered Dec 27, 2009 at 1:56

bobincebobince

518k102 gold badges644 silver badges825 bronze badges

Lets see a very simple example of magic method __contains__ :

Suppose I have class Player and my __init__ method takes one string argument name. In main I have created an object [obj1] of class Player.

Now if I want to know if my obj1 [in this case attribute name of obj1] contains a particular string, substring or an alphabet, I have to implement __contains__ method as shown in the example.

If my class has __contains__ method I can call built-in operator in on my custom objects as shown in the example.

   class Player[]:

    def __init__[self, name]:
        self.name=name

    def __contains__[self, substring]:
        if substring in self.name:
            return True
        else:
            return False

obj1=Player["Sam"]
print ['am' in obj1]    ----> True
print ['ami' in obj1]   ----> False

answered Jul 29, 2016 at 10:00

N RandhawaN Randhawa

7,9833 gold badges41 silver badges47 bronze badges

Not the answer you're looking for? Browse other questions tagged python or ask your own question.