split sentences with multiple characters and join them at the end of each sentence

Question

I have a text file with 1000 sentences. I splitted the sentences from '.' but there are also '?' and '!' available in those sentences. I need to split them as well and also join those characters at the end of those sentences. eg: text = "I have a friend. I have many friends. I am very happy today?Are you happy. I wish you were." Output:

I have a friend.
I have many friends!
I am very happy today.
Are you happy?
I wish you were.

The code I've tried is

textsentences = text.split('.')
I have tried this code.
with open("file.txt",'w') as writefile:
    for line in textsentences:
        line = line.strip()
        writefile.write("%s . \n" % line)

It works only for one character.

Answer 1

This should work. The line_start variable is to avoid unnecessary spaces at beginning of the sentence:

text = "I have a friend. I have many friends! I am very happy today. Are you happy? I wish you were."
line_start = False
with open("file.txt", 'w') as writefile:
    for i in range(len(text)):
        if text[i].isalnum() or text[i] == ' ':
            if line_start == True and text[i] == ' ':
                line_start = False
                continue
            writefile.write(text[i])
        else:
            writefile.write(text[i] +'\n')
            line_start = True

Output: file.txt

I have a friend.
I have many friends!
I am very happy today.
Are you happy?
I wish you were.