How to check if array is not empty? [duplicate]

This question already has answers here: How do I check if a list is empty? (27 answers) Closed 4 years ago.

How to check if the array is not empty? I did this:

if not self.table[5] 开发者_开发问答is None:

Is this the right way?

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There's no mention of numpy in the question. If by array you mean list, then if you treat a list as a boolean it will yield True if it has items and False if it's empty.

l = []

if l:
    print "list has items"

if not l:
    print "list is empty"

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with a as a numpy array, use:

if a.size:
   print('array is not empty')

(in Python, objects like [1,2,3] are called lists, not arrays.)

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len(self.table) checks for the length of the array, so you can use if-statements to find out if the length of the list is greater than 0 (not empty):

Python 2:

if len(self.table) > 0:
    #Do code here

Python 3:

if(len(self.table) > 0):
    #Do code here

It's also possible to use

if self.table:
    #Execute if self.table is not empty
else:
    #Execute if self.table is empty

to see if the list is not empty.

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if self.table:
    print 'It is not empty'

Is fine too

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print(len(a_list))

As many languages have the len() function, in Python this would work for your question.

If the output is not 0, the list is not empty.

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If you are talking about Python's actual array (available through import array from array), then the principle of least astonishment applies and you can check whether it is empty the same way you'd check if a list is empty.

from array import array
an_array = array('i') # an array of ints

if an_array:
    print("this won't be printed")

an_array.append(3)

if an_array:
    print("this will be printed")

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I can't comment yet, but it should be mentioned that if you use numpy array with more than one element this will fail:

if l:
    print "list has items"

elif not l:
    print "list is empty"

the error will be:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

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An easy way is to use Boolean expressions:

if not self.table[5]:
    print('list is empty')
else:
    print('list is not empty')

Or you can use another Boolean expression :

if self.table[5] == []:
    print('list is empty')
else:
    print('list is not empty')