How to use Python 'in' operator to check my list/tuple contains each of the integers 0, 1, 2?

问题

How do I use the Python in operator to check my list/tuple sltn contains each of the integers 0, 1, and 2?

I tried the following, why are they both wrong:

# Approach 1
if ("0","1","2") in sltn:
     kwd1 = True

# Approach 2
if any(item in sltn for item in ("0", "1", "2")):
     kwd1 = True

Update: why did I have to convert ("0", "1", "2") into either the tuple (1, 2, 3)? or the list [1, 2, 3]?

回答1:

if ("0","1","2") in sltn

You are trying to check whether the sltn list contains the tuple ("0","1","2"), which it does not. (It contains 3 integers)

But you can get it done using #all() :

sltn = [1, 2, 3] # list
tab = ("1", "2", "3") # tuple

print(all(int(el) in sltn for el in tab)) # True

回答2:

Using the in keyword is a shorthand for calling an object's __contains__ method.

>>> a = [1, 2, 3]
>>> 2 in a
True
>>> a.__contains__(2)
True

Thus, ("0","1","2") in [0, 1, 2] asks whether the tuple ("0", "1", "2") is contained in the list [0, 1, 2]. The answer to this question if False. To be True, you would have to have a list like this:

>>> a = [1, 2, 3, ("0","1","2")]
>>> ("0","1","2") in a
True

Please also note that the elements of your tuple are strings. You probably want to check whether any or all of the elements in your tuple - after converting these elements to integers - are contained in your list.

To check whether all elements of the tuple (as integers) are contained in the list, use

>>> sltn = [1, 2, 3]
>>> t = ("0", "2", "3")
>>> set(map(int, t)).issubset(sltn)
False

To check whether any element of the tuple (as integer) is contained in the list, you can use

>>> sltn_set = set(sltn)
>>> any(int(x) in sltn_set for x in t)
True

and make use of the lazy evaluation any performs.

Of course, if your tuple contains strings for no particular reason, just use
(1, 2, 3) and omit the conversion to int.

回答3:

To check whether your sequence contains all of the elements you want to check, you can use a generator comprehension in a call to all:

if all(item in sltn for item in ("0", "1", "2")):
    ...

If you're fine with either of them being inside the list, you can use any instead:

if any(item in sltn for item in ("0", "1", "2")):
    ...

回答4:

In case you don't want waste time and iterate through all the data in your list, as widely suggested around here, you can do as follows:

a = ['1', '2', '3']
b = ['4', '3', '5']

test = set(a) & set(b)
if test:
    print('Found it. Here it is: ', test)

Of course, you can do if set(a) & set(b). I didn't do that for demonstration purposes. Note that you shouldn't replace & with and. They are two substantially different operators.

The above code displays:

Found it. Here it is:  {'3'}

来源：https://stackoverflow.com/questions/35302215/how-to-use-python-in-operator-to-check-my-list-tuple-contains-each-of-the-inte

标签

python

python-3.x

contains