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

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