Is it better to use is or for number comparison in Python

Question

Is it better to use the  is  operator or the      operator to compare two numbers in Python   Examples    gt  gt  gt  a   1  gt  gt  gt  a is 1 True  gt  gt  gt  a    1 True  gt  gt  gt  a is 0 False  gt  gt  gt  a    0 False

User · Answer

That will only work for small numbers and I'm guessing it's also implementation-dependent. Python uses the same object instance for small numbers (iirc <256), but this changes for bigger numbers.

>>> a = 2104214124
>>> b = 2104214124
>>> a == b
True
>>> a is b
False

So you should always use == to compare numbers.

User · Answer

Use       Sometimes  on some python implementations  by coincidence  integers from -5 to 256 will work with is  in CPython implementations for instance   But don t rely on this or use it in real programs

User · Answer

gt  gt  gt  2    2 0 True  gt  gt  gt  2 is 2 0 False   Use

User · Answer

is what you want   is  just happens to work on your examples

User · Answer

gt  gt  gt  a   255556  gt  gt  gt  a    255556 True  gt  gt  gt  a is 255556 False   I think that should answer it  -   The reason is that some often-used objects  such as the booleans True and False  all 1-letter strings and short numbers are allocated once by the interpreter  and each variable containing that object refers to it  Other numbers and larger strings are allocated on demand  The 255556 for instance is allocated three times  every time a different object is created  And therefore  according to is  they are not the same

User · Answer

Others have answered your question  but I ll go into a little bit more detail   Python s is compares identity - it asks the question  is this one thing actually the same object as this other thing   similar to    in Java   So  there are some times when using is makes sense - the most common one being checking for None  Eg  foo is None  But  in general  it isn t what you want       on the other hand  asks the question  is this one thing logically equivalent to this other thing   For example    gt  gt  gt   1  2  3      1  2  3  True  gt  gt  gt   1  2  3  is  1  2  3  False   And this is true because classes can define the method they use to test for equality    gt  gt  gt  class AlwaysEqual object           def   eq   self  other               return True      gt  gt  gt  always equal   AlwaysEqual    gt  gt  gt  always equal    42 True  gt  gt  gt  always equal    None True   But they cannot define the method used for testing identity  ie  they can t override is

[python] Is it better to use "is" or "==" for number comparison in Python?

Examples related to python