(index := bisect.bisect_left(container, value)) < len(container) Here is an example of code using Python 3.8 and above syntax: import bisect Using bisect module on my machine is about 12 times faster than using 'in' operator. So you sort data once and then you can use bisect. Keep in mind that using bisect module data must be sorted. However, if you are going to check for more than once then I recommend using bisect module. If you are going to check if value exist in the collectible once then using 'in' operator is fine. If there are duplicates and you want all the indexes then you can use enumerate() instead: ) if x=2] # => index always returns the lowest index.index(2) # => 1 However, note that if you have duplicates. ), )įor lists, there's also the index method that can sometimes be useful if you want to know where a certain element is in the list. Alternatively, you can use next((x for x in lst if. Which will return the first match or raise a StopIteration if none is found. If you only want the first thing that matches a condition (but you don't know what it is yet), it's fine to use a for loop (possibly using the else clause as well, which is not really well-known). In Python 3, filter doesn't return a list, but a generator-like object. Here you can see higher-order functions at work. By the way, the first one is exactly equivalent to matches = filter(fulfills_some_condition, lst) The latter will return a generator which you can imagine as a sort of lazy list that will only be built as soon as you iterate through it. You can use list comprehension or generator expressions for that: matches = That is, finding all elements in a sequence that meet a certain condition. As you know, you can use the in operator for that: 3 in # => True This is the use case you describe: Checking whether something is inside a list or not. For instance, 1 - 1/3 != 2/3.Īs for your second question: There's actually several possible ways if "finding" things in lists. Floating point values in particular may suffer from inaccuracy. For instance, "abc" and "ABC" do not match. The item must exactly match an item in the list. As for your first question: " if item is in my_list:" is perfectly fine and should work if item equals one of the elements inside my_list.
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