Function that retrieves and returns letters from a list of lists

I'm writing a function that needs to go through a list of lists, collect all letters uppercase or lowercase and then return a list with 1 of each letter that it found in order. If the letter appears multiple times in the list of lists the function only has to report the first time it sees the letter.

For example, if the list of lists was [['.', 'M', 'M', 'N', 'N'],['.', '.', '.', '.', 'g'], ['B', 'B', 'B', '.','g']] then the function output should return ["M","N","g","B"].

The code I have so far seems like it could work but it doesn't seem to be working. Any help is appreciated

def get_symbols(lot):

    symbols = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

    newlot = []

    for i in lot:
        if i == symbols:
            newlot.append(symbols)
            return newlot
        else:
            return None

Solution

There are a few things wrong with your code. You are using return in the wrong place, looping only over the outer list (not over the items in the sublists) and you were appending symbols to newlot instead of the matched item.

def get_symbols(lot):

    symbols = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ' # You should define this OUTSIDE of the function

    newlot = []

    for i in lot: # You are iterating over the outer list only here
        if i == symbols: # == does not check if an item is in a list, use `in` here
            newlot.append(symbols) # You are appending symbols which is the alphabet
            return newlot # This will cause your function to exit as soon as the first iteration is over
        else:
            return None # No need for this

You can use a double for loop and use in to check if the character is in symbols and isn't already in newlot:

l = [['.', 'M', 'M', 'N', 'N'],['.', '.', '.', '.', 'g'], ['B', 'B', 'B', '.','g']]
symbols = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

def get_symbols(lot):

    newlot = []

    for sublist in lot:
        for i in sublist:

            if i in symbols and i not in newlot:
                newlot.append(i)

    return newlot

This is the output for your list:

>>> get_symbols(l)
['M', 'N', 'g', 'B']