Difference between the in keyword and __contains__ in Python
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I was wondering if some one could explain the difference between the "in" keyword of Python and the contains method
I was working with a sample list and found this behavior. When are the two supposed to be used? Is there some efficiency that can be achieved if I use one over the other.
>>> my_list = ["a", "b", "c"] >>> my_list.__contains__("a") True >>> "a" in my_list True
From the docs:
For the list and tuple types, x in y is true if and only if there exists an index i such that x == y[i] is true.
string types, x in y is true if and only if x is a substring of y. An equivalent test is y.find(x) != -1.
For user-defined classes which define the
__contains__()method, x in y is true if and only if
For user-defined classes which do not define
__contains__()but do define
__iter__(), x in y is true if some value z with x == z is produced while iterating over y. If an exception is raised during the iteration, it is as if in raised that exception.
Lastly, the old-style iteration protocol is tried: if a class defines
__getitem__(), x in y is true if and only if there is a non-negative integer index i such that x == y[i], and all lower integer indices do not raise
Functionality of Python `in` vs. `__contains__`, import dis >>> class test(object): def __contains__(self, other): return 6 CALL_FUNCTION 0 (0 positional, 0 keyword pair) 9 COMPARE_OP 6 (in) so if the comparison operator is used in a Boolean context (e.g., in the� There are total 33 keywords in Python 3.6. To get the keywords list on your operating system, open command prompt (terminal on Mac OS) and type “Python” and hit enter. After that type help() and hit enter. Type keywords to get the list of the keywords for the current python version running on your operating system. Chaitanyas-MacBook-Pro
__contains__() method of an an object is called when you use the
For lists this is pre-defined, but you can also define your own class, add a
__contains__ method and use
in on the instances of that class.
You should be using
in and not call
9. Classes — Python 3.8.5 documentation, Objects can contain arbitrary amounts and kinds of data. Of course, the __ init__() method may have arguments for greater flexibility. In that By definition, all attributes of a class that are function objects define corresponding methods of its� Python Keywords. Keywords are special words which are reserved and have a specific meaning. Python has a set of keywords that cannot be used as variables in programs. All keywords in Python are case sensitive. So, you must be careful while using them in your code. We’ve just captured here a snapshot of the possible Python keywords.
Like most magic methods, the
__contains__ method is not meant to be called directly. The reason
__contains__ exists is precisely so that you can write
obj in container instead of having to use method-call syntax. So you should use
obj in container.
3. Data model — Python 2.7.18 documentation, (The value of an immutable container object that contains a reference to a mutable Their definition may change in the future. __defaults__ func_defaults number of positional arguments; bit 0x08 is set if the function uses the **keywords� Python 3.x introduced some Python 2-incompatible keywords and features that can be imported via the in-built __future__ module in Python 2. It is recommended to use __future__ imports it if you are planning Python 3.x support for your code. For example, if we want Python 3.x’s integer division behavior in Python 2, we can import it via.
"a" in my_list actually calls
__contains__ method of
my_list if defined.
__contains__ is not defined then
__getitem__ is used.
3. Data model — Python 3.8.5 documentation, (The value of an immutable container object that contains a reference to a mutable object __doc__. The function's documentation string, or None if unavailable; not Any other keyword arguments that are specified in the class definition are� It depends on the class how it does the check. For the builtin list it uses the == operator; otherwise you couldn't e.g. use 'something' in somelist safely.. To be more specific, it check if the item is equal to an item in the list - so internally it's most likely a hash(a) == hash(b) comparison; if the hashes are equal the objects itself are probably compared, too.
Programming FAQ — Python 3.8.5 documentation, How can I pass optional or keyword parameters from one function to another? What is the difference between arguments and parameters? My class defines __del__ but it is not called when I delete the object. a custom-made config file that only contains those built-in modules which are actually used in the program. Note about the speed differences in Python 2 and 3. Some people pointed out the speed difference between Python 3’s range() and Python2’s xrange(). Since they are implemented the same way one would expect the same speed. However the difference here just comes from the fact that Python 3 generally tends to run slower than Python 2.
Python's Instance, Class, and Static Methods Demystified – Real , Let's begin by writing a (Python 3) class that contains simple examples for all three method Let's compare that to the second method, MyClass.classmethod . class Pizza: def __init__(self, ingredients): self.ingredients = ingredients def� Difference between dir() and help() In Python, help() is a super useful built-in function that can be used to return the Python documentation of a particular object, method, attributes, etc.
Python Tutorial: Magic Methods, Our class contains the __str__ and __repr__ methods as well. The instances of the class Length contain length or distance information. The attributes of an�