如何检查数组是否为空? [重复]

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


This question already has an answer here:

这个问题在这里已有答案:

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

如何检查数组是否为空?我这样做了:

if not self.table[5] is None:

Is this the right way?

这是正确的方法吗?

8 个解决方案

#1


45  

with a as a numpy array, use:

使用a作为numpy数组,使用:

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

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

(在Python中,像[1,2,3]这样的对象被称为列表,而不是数组。)

#2


44  

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.

问题中没有提到numpy。如果你通过数组表示列表,那么如果你将列表视为布尔值,如果它有项目则会产生True,如果它是空的则会产生False。

l = []

if l:
    print "list has items"

if not l:
    print "list is empty"

#3


6  

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

Is fine too

很好

#4


3  

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):

len(self.table)检查数组的长度,因此您可以使用if语句来查明列表的长度是否大于0(非空):

Python 2:

Python 2:

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

Python 3:

Python 3:

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

It's also possible to use

它也可以使用

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.

查看列表是否为空。

#5


1  

An easy way is to use Boolean expressions:

一种简单的方法是使用布尔表达式:

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

Or you can use another Boolean expression :

或者您可以使用另一个布尔表达式:

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

#6


1  

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

我还不能评论,但应该提到的是,如果你使用带有多个元素的numpy数组,这将失败:

if l:
       print "list has items"

elif not l:
    print "list is empty"

the error will be:

错误将是:

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

#7


0  

print(len(a_list))

打印(LEN(的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.

由于许多语言都具有len()函数,因此在Python中这可以解决您的问题。如果输出不为0,则列表不为空。

#8


0  

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.

如果你在谈论Python的实际数组(通过数组中的import数组提供),那么应用最少惊讶的原则,你可以检查它是否为空,就像检查列表是否为空一样。

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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