在嵌套列表中使用.index（）函数

Question

I am trying to make a program that finds a certain value in a nested list, so I wrote this code:

list = [['S', 'T', 'U', 'T'], ['O', 'P', 'Q', 'R']]

However, when I inputted

list.index('O')

It gave me an error message saying

Traceback (most recent call last):
File "<pyshell#11>", line 1, in <module>
list.index('O')
ValueError: 'O' is not in list

Any ideas?

Answer 1

Well it is really simple, 'O' is not in the list, it only contains the other lists. Here is an example:

list_you_have = [['S', 'T', 'U', 'T'], ['O', 'P', 'Q', 'R']]
print list_you_have.index(['O','P','Q','R']) #outputs 1

Now if you do it like:

print list_you_have[1].index('O') # it outputs 0 because you're pointing to 
#list which acctualy contains that 'O' char.

Now a function for nested char search would be

def nested_find(list_to_search,char):
    for i, o in enumerate(list_to_search):
        if char in o:
            print "Char %s found at list %s at index %s" % (char, i, o.index(char))

Or maybe an even simpler solution as @zondo commented would be:

def nested_find(list_to_search,char):
    newlist = sum(list_to_search, [])
    if char in newlist:
        print "Char %s is at position %s" % (char, newlist.index(char))

Answer 2

您可以单行解决问题：

print item in reduce(lambda x, y: x + y, nestedlists)