Replace only whole words using a dictionary (file)

Question

I'm pretty new to python so please forgive me,if this is really obvious. I would like to replace all the words in file with alternative words based on a dictionary ( or dictionary file). I've been through a number of other posts and this code ( below) works quite well. However, it will also replace substrings.

text = "strings.txt"
fields = {"Cat": "Hello", "Hat": "Goodbye"}


for line in fileinput.input(text, inplace=True):
    line = line.rstrip()
    if not line:
        continue
    for f_key, f_value in fields.items():
        if f_key in line:
            line = line.replace(f_key, f_value)
    print (line)

So, caterpillar will become Helloerpillar and hatemonger will become Goodbyemonger. I would like substrings to be left alone, so only the full words will be replaced. Can anyone advise me on how to do this?

Also.... This is less important but I have also tried to get the script to read the dictionary from a separate file. This isn't so important but it would be nice to have.

I have tried to modify the script in the following way without luck.

    import json
  
with open('dictionary.txt') as f:
    data = f.read()

text = "strings.txt"
fields = data

for line in fileinput.input(text, inplace=True):
    line = line.rstrip()
    if not line:
        continue
    for f_key, f_value in fields.items():
        if f_key in line:
            line = line.replace(f_key, f_value)
    print (line)

any advice that you could provide on either of these problems ( especially the first) would be greatly appreciated.

Thanks

Answer 1

You can do:

fields = {"Cat": "Hello", "Hat": "Goodbye"}
s = "This Is A Catterpilar Chatting With A Cat"


s =   ' '.join([fields[w] if w in fields else w for w in s.split(' ')])

output:

'This Is A Catterpilar Chatting With A Hello'

What the line do is split the sentence into words, replace every word by its equivalent if it is in the fields dict else leave it as is, then join all words into a new sentence.

For simplicity sake, all words begin with a capital, but you can handle this easily aa second step.