python - Regular expression of a sentence -

i'm trying write regular expression represent sentence following conditions: starts capital letter, ends period (and 1 period can appear), , allowed contain comma or semi-colon, when does, must appear (letter)(semicolon)(space) or (letter)(comma)(space).

i've got capital letter , period down. have idea code think i'm not getting syntax right...

in english, expression sentence looks this:

(capital letter) ((lowercase letter)(space) ((lowercase letter)(comma)(space))*  ((lowercase letter)(semicolon)(space)* )* (period) 

i realize ignores case first letter of sentence followed comma or semicolon, it's safe ignore case.

now when try code in python, try following (i've added whitespace make things easier read):

sentence = re.compile("^[a-z]  [a-z\\s  (^[a-z];\\s$)* (^[a-z],\\s$)*]*  \.$") 

i feel it's syntax issue... i'm not sure if i'm allowed have semicolon , comma portions inside of parentheses.

sample inputs match definition:

"this sentence." "hello, world." "hi there; hi there." 

sample inputs not match definition:

"i ate breakfast." "this , sentence." "what time it?" 

this match said above.

^"[a-z][a-z]*(\s*|[a-z]*|(?<!\s)[;,](?=\s))*[.]"$? => demo

this match:

"this sentence." "hello, world." "hi there; hi there." 

this won't match:

"i ate breakfast." "this , sentence." "what time it?" "i ,d am." "i a,d am." 

if don't need " remove regex.

---

if need regex in python, try

re.compile(r'^[a-z][a-z]*(\s*|[a-z]*|(?<!\s)[;,](?=\s))*[.]$')

python demo

import re tests = ["this sentence." ,"hello, world." ,"hi there; hi there." ,"i ate breakfast." ,"this , sentence." ,"what time it?"] rex = re.compile(r'^[a-z][a-z]*(\s*|[a-z]*|(?<![\s])[;,])*[.]$') test in tests:     print rex.match(test) 

output

<_sre.sre_match object @ 0x7f31225afb70> <_sre.sre_match object @ 0x7f31225afb70> <_sre.sre_match object @ 0x7f31225afb70> none none none