如果列表包含一个项目，则列表等于项目

Question

I don't know how to formulate the question correctly: I have a list of lists, which contains multiple items.

mylist=[['a','b','c','₾'],['x','t','f','₾'],['a','d'],['r','y'],['c','₾'],['a','b','c','i'],['h','j','l','₾']]

If any of the lists contains symbol '₾', I want to append the symbol to another list, else append None.

result=[]
for row in mylist:
    for i in row:
        if i=='₾':
            result.append(i)
        else:
            result.append(None)
result

But I want to get this result:

result=['₾','₾',None,None,'₾',None,'₾']

Answer 1

That would be:

result = ['₾' if '₾' in sublist else None for sublist in mylist]

Answer 2

result = []
for row in mylist:
    if '₾' in row:
        result.append('₾')
    else:
        result.append(None)

Answer 3

>>> mylist=[['a','b','c','₾'],['x','t','f','₾'],['a','d'],['r','y'],['c','₾'],['a','b','c','i'],['h','j','l','₾']]
>>> c = '₾'
>>> [c if c in row else None for row in mylist]
['₾', '₾', None, None, '₾', None, '₾']

That is, you can use a list comprehension: for each list in mylist , use ₾ if it is in the list, or else None :

c = '₾'
result = [c if c in row else None for row in mylist]

There were several problems with the loop in the posted code:

• After finding a ₾, the inner loop should break, stop searching the rest
• The value should only be None when all values were not ₾

Here's one way to fix the loop:

result = []
for row in mylist:
    for item in row:
        if item == '₾':
            result.append(item)
            break
    else:
        result.append(None)

Notice here that else belongs to the inner for , not the if . The meaning of this is that if the inner loop never reached a break , then this else will be executed. This fixes both of the problems I mentioned earlier.

Answer 4

A small edit to your code can be done to get the desired result

mylist=[['a','b','c','₾'],['x','t','f','₾'],['a','d'],['r','y'],['c','₾'],['a','b','c','i'],['h','j','l','₾']]

result=[]
for row in mylist:
    if '₾' in row:
        result.append(i)
    else:
        result.append(None)
result

Output

['₾', '₾', None, None, '₾', None, '₾']

The above code can be reduced into a line of List Comprehension

['₾' if '₾' in row else None for row in mylist]