Man*_*tis 66 python interpreter comments interpreted-language
我问这个是因为我使用Python,但它也适用于其他解释语言(Ruby,PHP,JavaScript).
每当我在代码中留下评论时,我是否会放慢口译员的速度？根据我对解释器的有限理解,它以字符串形式读取程序表达式,然后将这些字符串转换为代码.似乎每次解析评论时都会浪费时间.
是这样的吗？在解释语言中是否有一些评论惯例,或者效果可以忽略不计？
Lup*_*uch 79
对于Python的情况,源文件在执行之前被编译(.pyc文件),并且在过程中删除了注释.因此,如果您有足够的注释,注释可能会减慢编译时间,但它们不会影响执行时间.
Ric*_*haw 24
好吧,我写了一个这样的短python程序:
for i in range (1,1000000):
a = i*10
这个想法是,做一个简单的计算次数.
通过计时,运行需要0.35±0.01秒.
然后我用这样插入的整个King James Bible重写了它:
for i in range (1,1000000):
"""
The Old Testament of the King James Version of the Bible
The First Book of Moses: Called Genesis
1:1 In the beginning God created the heaven and the earth.
1:2 And the earth was without form, and void; and darkness was upon
the face of the deep. And the Spirit of God moved upon the face of the
waters.
1:3 And God said, Let there be light: and there was light.
...
...
...
...
Even so, come, Lord Jesus.
22:21 The grace of our Lord Jesus Christ be with you all. Amen.
"""
a = i*10
这次运行需要0.4±0.05秒.
所以答案是肯定的.循环中4MB的注释会产生可测量的差异.
ken*_*ytm 19
注释通常在解析阶段或之前被删除,并且解析非常快,因此有效注释不会减慢初始化时间.
日常使用的效果可以忽略不计。测试很容易，但如果您考虑一个简单的循环，例如：
For N = 1 To 100000: Next
您的计算机可以比您眨眼的速度更快地处理（数到 100,000）。忽略以某个字符开头的一行文本会快 10,000 倍以上。
别担心。
这取决于解释器的实现方式。大多数合理的现代解释器在任何实际执行之前至少对源代码进行一些预处理，这将包括删除注释，以便从那时起它们没有区别。
曾几何时，当内存受到严重限制时（例如，64K 的总可寻址内存和用于存储的盒式磁带），您不能将这样的事情视为理所当然。在 Apple II、Commodore PET、TRS-80 等时代，程序员显式删除注释（甚至空格）以提高执行速度是相当常规的。这也是仅在时间通常采用的许多源代码级黑客的一个1。
当然，这也有助于这些机器的 CPU 一次只能执行一条指令，时钟速度约为 1 MHz，并且只有 8 位处理器寄存器。即使是现在只能在垃圾箱中找到的机器也比那些机器快得多，甚至都不好笑......
1. 再举一个例子，在 Applesoft 中，根据您如何编号行，您可能会增加或减少一点速度。如果没记错的话，速度增益是当 goto 语句的目标是 16 的倍数时。
像Rich这样的脚本做了一些评论(只有大约500kb文本):
# -*- 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
根据大卫的评论编辑:
-*- 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 = """
# <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
# blah blah...
# --></body></html>
"""
tabhistorylesson = """
# <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
# blah blah...
# --></body></html>
"""
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
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