Do comments slow down an interpreted language?

Question

I am asking this because I use Python, but it could apply to other interpreted languages as well (Ruby, PHP, JavaScript).

Am I slowing down the interpreter whenever

Answer 1

Did up a script like Rich's with some comments (only about 500kb text):

# -*- coding: iso-8859-15 -*-
import timeit

no_comments = """
a = 30
b = 40
for i in range(10):
    c = a**i * b**i
"""
yes_comment = """
a = 30
b = 40

# full HTML from http://en.wikipedia.org/
# wiki/Line_of_succession_to_the_British_throne

for i in range(10):
    c = a**i * b**i
"""
loopcomment = """
a = 30
b = 40

for i in range(10):
    # full HTML from http://en.wikipedia.org/
    # wiki/Line_of_succession_to_the_British_throne

    c = a**i * b**i
"""

t_n = timeit.Timer(stmt=no_comments)
t_y = timeit.Timer(stmt=yes_comment)
t_l = timeit.Timer(stmt=loopcomment)

print "Uncommented block takes %.2f usec/pass" % (
    1e6 * t_n.timeit(number=100000)/1e5)
print "Commented block takes %.2f usec/pass" % (
    1e6 * t_y.timeit(number=100000)/1e5)
print "Commented block (in loop) takes %.2f usec/pass" % (
    1e6 * t_l.timeit(number=100000)/1e5)

C:\Scripts>timecomment.py
Uncommented block takes 15.44 usec/pass
Commented block takes 15.38 usec/pass
Commented block (in loop) takes 15.57 usec/pass

C:\Scripts>timecomment.py
Uncommented block takes 15.10 usec/pass
Commented block takes 14.99 usec/pass
Commented block (in loop) takes 14.95 usec/pass

C:\Scripts>timecomment.py
Uncommented block takes 15.52 usec/pass
Commented block takes 15.42 usec/pass
Commented block (in loop) takes 15.45 usec/pass

Edit as per David's comment:

 -*- coding: iso-8859-15 -*-
import timeit

init = "a = 30\nb = 40\n"
for_ = "for i in range(10):"
loop = "%sc = a**%s * b**%s"
historylesson = """
#  
"""
tabhistorylesson = """
    #  
"""

s_looped = init + "\n" + for_ + "\n" + tabhistorylesson + loop % ('   ','i','i')
s_unroll = init + "\n"
for i in range(10):
    s_unroll += historylesson + "\n" + loop % ('',i,i) + "\n"
t_looped = timeit.Timer(stmt=s_looped)
t_unroll = timeit.Timer(stmt=s_unroll)

print "Looped length: %i, unrolled: %i." % (len(s_looped), len(s_unroll))

print "For block takes %.2f usec/pass" % (
    1e6 * t_looped.timeit(number=100000)/1e5)
print "Unrolled it takes %.2f usec/pass" % (
    1e6 * t_unroll.timeit(number=100000)/1e5)

C:\Scripts>timecomment_unroll.py
Looped length: 623604, unrolled: 5881926.
For block takes 15.12 usec/pass
Unrolled it takes 14.21 usec/pass

C:\Scripts>timecomment_unroll.py
Looped length: 623604, unrolled: 5881926.
For block takes 15.43 usec/pass
Unrolled it takes 14.63 usec/pass

C:\Scripts>timecomment_unroll.py
Looped length: 623604, unrolled: 5881926.
For block takes 15.10 usec/pass
Unrolled it takes 14.22 usec/pass