pyCorrectSentences

intext = "mary ,  had a little   lamb!!isn't it cute ??!!   it followed  her to school;; ate all her sandwiches. oh dear"

newtext = ""

start_sentence = True
spctr = 1
lastch = " "
lastnonsp = ""

for ch in intext:
    if start_sentence:
        if ch in [".", "!", "?"]:
            if ch == lastch:
                continue
            if lastch == " ":
                newtext = newtext.rstrip(' ')
            lastch = ch
            newtext += ch
            newtext += " "
            spctr = 1
            continue
        if ch == ' ':
            spctr += 1
            if spctr == 1:
                newtext += ch
            lastch = ch
            continue
        if not spctr:
            newtext += " "
        ch = ch.upper()
        newtext += ch
        start_sentence = False
        lastch = ch
        continue

    if ch in [".", "!", "?"]:
        if lastch == " ":
            newtext = newtext.rstrip()
        start_sentence = True
    if ch in [',', ':', ';']:
        if lastnonsp == ch:
            continue
        newtext = newtext.rstrip()
        newtext += ch
        newtext += " "
        lastnonsp = ch
        lastch = " "
        continue
    if ch == " " and lastch == " ":
        continue

    if ch != " ":
        spctr = 0

    lastch = ch
    newtext += ch

# ensure sentence ends with a sentence terminator
newtext = newtext.rstrip()
if newtext[-1] not in [".", "!", "?"]:
    newtext += "."
print(newtext)

# in = "mary ,  had a little   lamb!!isn't it cute ??!!   it followed  her to school;; ate all her sandwiches. oh dear"
# Out: "Mary, had a little lamb! Isn't it cute?! It followed her to school; ate all her sandwiches. Oh dear."