Python Forum

I'm just learning Python by developing an anagram finder.

After a bit of debugging it seems that if I check "if token not in words" then the words dictionary treats its elements as List items.

But if I assign a value without doing the "if" check, the values are treated as Strings (rather than a List of strings).

Is there somewhere I can research why the behavior changes? Is there a way to force the dictionary to make the values Lists?

I'm using PyCharm 2019.3.4 for Mac with Python 3.7.2

# This code block treats words[] values as List items, allowing append to work
words = dict()
token: str ="acto"
if token not in words:
    words[token] = ["coat"]
else:
    words[token].append("coat")

words[token].append("taco") #In this code block, "taco" is appended to the List associated with the "acto" key -> ['coat', 'taco']

for x in words:
    print (words[x])

# This code block treats words[] values as Strings items.  Append does not work
words = dict()
token: str ="acto"
words[token] = ["coat"]
words[token].append("taco") #blows up because String has no append method.

Please, post full traceback you get, in error tags. There is something else, because your code works:
the second code works

words = dict()
token:str = "acto"
words[token] = ["coat"]
words[token].append("taco")
print(words)

Output:
{'acto': ['coat', 'taco']}

Hi Buran

Thanks for helping. Here's the snippet and the error message

words2 = dict()
token: str ="acto"
words2[token]="coat"
words2[token].append("taco") #Line 16

Traceback (most recent call last):
File "/Users/Library/Preferences/PyCharmCE2019.3/scratches/QuickDictionary.py", line 16, in <module>
words2[token].append("taco")
AttributeError: 'str' object has no attribute 'append'
['coat', 'taco']
<re.Match object; span=(0, 0), match=''>

Process finished with exit code 1

If you want the dictionary to contain lists you need to add lists. "coat" is a string. ["coat"] is a list that contains a string. You can append to a list of strings. You cannot append to a string. Your first two examples run correctly because they initially add a list to the dictionary. The final example fails because it adds a word. I think you problem is a typo.

(Mar-30-2020, 01:16 AM)deanhystad Wrote: [ -> ]If you want the dictionary to contain lists you need to add lists. "coat" is a string. ["coat"] is a list that contains a string. You can append to a list of strings. You cannot append to a string. Your first two examples run correctly because they initially add a list to the dictionary. The final example fails because it adds a word. I think you problem is a typo.

Thanks for catching that - it did the trick.