如何检查python列表中的最后三个元素-它们是否是整数？

Question

I am using Python, version 2.7.2.

I have a task to check whether the last three elements from a list are integer? For example:

mylist = [String, Large_string_containing_integers_inside_it, 80, 40, 50]

For above list I want to check whether the last three elements are integer or not. How can I do this?

Here is the code I am testing:

#!/usr/bin/python

line = ['MKS_TEST', 'Build', 'stability:', '1', 'out', 'of', 'the', 'last', '2', 'builds', 'failed.', '80', '40', '50']

if all(isinstance(i, int) for i in line[-3:]):
    job_name = line[0]
    warn = line[-3]
    crit = line[-2]
    score = line[-1]
    if score < crit:
        print ("CRITICAL - Health Score is %d" % score)
    elif (score >= crit) and (score <= warn):
        print ("WARNING - Health Score is %d" % score)
    else:
        print ("OK - Health Score is %d" % score)

Answer 1

Use the built in isinstance and all functions, along with list slicing.

if all(isinstance(i, int) for i in mylist[-3:]):
    # do something
else:
    # do something else

• all checks if all elements in the given iterable evaluate to True .
• isinstance checks if the given object is an instance of the second parameter
• mylist[-3:] returns the last three elements of mylist

Also, if you're using Python 2 and have very large numbers in your list, check for the long (long integer) type as well.

if all(isinstance(i, (int, long)) for i in mylist[-3:]):
    pass

This prevents numbers like 10**100 from breaking the condition.

If, however, your last three elements are strings, you have two options.

If you know none of the numbers are exceedingly large, you can use the isdigit string method.

if all(i.isdigit() for i in mylist[-3:]):
    pass

However, if they can be very large (around or over 2**31 ), use a try/except block and the built in map function.

try:
    mylist[-3:] = map(int, mylist[-3:])
    # do stuff
except ValueError:
    pass

• try defines the block of code to execute
• except Exception catches the given exception and handles it without raising an error (unless told to do so)
• map applies a function to each element of an iterable and returns the result.