Return Subset of List that Matches Condition

问题:

Let's say I have a list of ints:

listOfNumbers = range(100)

And I want to return a list of the elements that meet a certain condition, say:

def meetsCondition(element):
    return bool(element != 0 and element % 7 == 0)

What's a Pythonic way to return a sub-list of element in a list for which meetsCondition(element) is True?

A naive approach:

def subList(inputList):
    outputList = []

    for element in inputList:
        if meetsCondition(element):
            outputList.append(element)

    return outputList

divisibleBySeven = subList(listOfNumbers)

Is there a simple way to do this, perhaps with with a list comprehension or set() functions, and without the temporary outputList?

回答1:

Use list comprehension,

divisibleBySeven = [num for num in inputList if num != 0 and num % 7 == 0]

or you can use the meetsCondition also,

divisibleBySeven = [num for num in inputList if meetsCondition(num)]

you can actually write the same condition with Python's truthy semantics, like this

divisibleBySeven = [num for num in inputList if num and num % 7]

---

alternatively, you can use filter function with your meetsCondition, like this

divisibleBySeven = filter(meetsCondition, inputList)