regarding ignore case sensitive of a string using regular expressions

Dear All In Perl when we are checking some conditions using regular expression we can ignore the case sensitive of a string using the following regular expression /(^[^a-z])|/|(\.\.)/i. But If I try to do this in Python I couldn't get any result. So Any body know regarding this

Doubt regarding exec function

Dear All, Php has exec function to run system commands and this function return last line of system command result. But in Python I can see only os.system() function to run system command but it doesn't return any result like php exec function. I want to know about php equivalent exec fu