How can this code be converted to a list comprehension?
pangram = "The quick brown fox jumps over the lazy dog"
lst = []
for char in pangram.casefold():
if char not in lst:
lst.append(char)
lst.sort()
print(''.join(lst))
I tried the following list comprehension but it is not working:
lst = [char for char in pangram.casefold if char not in lst]
It gives the following error
NameError: name 'lst' is not defined
Please suggest a solution.
It's possible to hack it with a list comprehension but you'll have to pre-define lst first:
In [1]: pangram = "The quick brown fox jumps over the lazy dog"
In [2]: lst = []
In [3]: [lst.append(char) for char in pangram.casefold() if char not in lst]
In [5]: lst.sort()
In [6]: print(''.join(lst))
abcdefghijklmnopqrstuvwxyz
But, this is really NOT a good practice because list comprehensions are meant for creating lists, not for mutating an existing one. In this solution, you are actually creating a list of None's because .append() returns None.
If the goal is just to get the unique values and order is not important, use a set instead. (I assume order is not important because you sort it after).
In [29]: pangram = "aAaabBBbbcCc"
In [30]: lst = list(set(pangram.casefold()))
In [31]: lst.sort()
In [32]: print(''.join(lst))
abc
In [33]: lst = []
In [34]: [lst.append(char) for char in pangram.casefold() if char not in lst]
Out[34]: [None, None, None]
In [35]: lst.sort()
In [36]: print(''.join(lst))
abc
There is no need for either a list or a comprehension. Use a set to automatically eliminate duplicates.
>>> pangram = "The quick brown fox jumps over the lazy dog"
>>> letters = set(pangram.casefold()) # the unique letters in pangram
>>> ''.join(sorted(letters))
' abcdefghijklmnopqrstuvwxyz'
In principle, the for loop can be converted to a list comprehension. This works by using a second set or list and exploiting that lst.append/set.add returns None, which allows evaluating a second expression when used with or.
>>> pangram = "The quick brown fox jumps over the lazy dog"
>>> seen = set()
>>> lst = [seen.add(char) or char for char in pangram.casefold() if char not in seen]
>>> lst.sort()
>>> ' abcdefghijklmnopqrstuvwxyz'