Use this as an example:
begin  # "try" block
    puts 'I am before the raise.'  
    raise 'An error has occured.' # optionally: `raise Exception, "message"`
    puts 'I am after the raise.'  # won't be executed
rescue # optionally: `rescue Exception => ex`
    puts 'I am rescued.'
ensure # will always get executed
    puts 'Always gets executed.'
end 
The equivalent code in Python would be:
try:     # try block
    print 'I am before the raise.'
    raise Exception('An error has occured.') # throw an exception
    print 'I am after the raise.'            # won't be executed
except:  # optionally: `except Exception as ex:`
    print 'I am rescued.'
finally: # will always get executed
    print 'Always gets executed.'