我想使用正则表达式（python 中的 re 模块）检测 C 之类的多行注释。
所以应该可以找到
/* this is my
first comment it also has a * in it.
Now I end my first comment */
int a = 3;
/* this is my second
multiline comment */
所以我需要使用 re 找到这两个多行注释。我想做
re.findall(r'exp', string )。应该表达什么？我尝试对这样的分组字符进行补码，r'\(\*[^(?:\*\))]*\*\)基本上将 *) 分组并检查其补码。但这不起作用。
一种可能的方式：
import re
ccode = '''/* this is my
first comment it also has a * in it.
Now I end my first comment */
int a = 3;
/* this is my second
multiline comment */'''
for comment in re.findall('/[*].*?[*]/', ccode, re.DOTALL):
print comment
给出：
/* this is my
first comment it also has a * in it.
Now I end my first comment */
/* this is my second
multiline comment */
话虽如此，如果您正在构建解析器，最好先在词法分析器中提取标记并将注释定义为解析器中的多标记结构。
仅使用正则表达式是不可行的 - 您可以创建状态机，因为您必须区分此类情况，例如：
你不会使用正则表达式来做到这一点。只是状态机。
我知道你想要 python，但前几天我在 erl 中做了类似的事情，所以她你走了。继续并转换为python。也许它不是最快/最好但足够好：
######################################################################################
#### Before going any further perform all 4 stages of preprocessing
#### described here http://gcc.gnu.org/onlinedocs/cpp/Initial-processing.html
############################# 1 - break file into lines ##############################
open FILE, $file or die "file [$file] was not found\n";
my @lines = <FILE>; # deletes \r from every line(\n stays on place)
close FILE;
################################ 2 - handle trigraphs ################################
foreach ( @lines )
{
s!\Q??=\E!#!g; #??= becomes #
s#\Q??/\E#\\#g; #??/ becomes \
s#\Q??'\E#^#g; #??' becomes ^
s#\Q??(\E#[#g; #??( becomes [
s#\Q??)\E#]#g; #??) becomes ]
s#\Q??!\E#|#g; #??! becomes |
s#\Q??<\E#{#g; #??< becomes {
s#\Q??>\E#}#g; #??> becomes }
s#\Q??-\E#~#g; #??- becomes ~
}
################################ 3 - merge continued lines ###########################
# everything in C/C++ may be spanned across many lines so we must merge continued
# lines to handle things correctly
# we do not delete lines that are merged with preceeding line - we just leave an
# empty line to preserve overal location of all things which will be needed later
# to properly report line numbers if we find sth that we are intersted in
for (my $i = 0; $i <= $#lines; $i++ )
{
# shows where continued line started ie. where to append following continued line(s)
state $appendHere; # acts also as an "append indicator"
my $continuedLine;
# theoretically continued line ends with \ but preprocessors accept \ followed by
# one or more whitespaces too so we accept it as well
if ( $lines[$i] =~ m#\\[ \t\v\f]*$# ) # merge with next line / continued line ?
{
$lines[$i] =~ s#\\[ \t\v\f]*$##; # delete \ with trailing whitespaces if any
$continuedLine = 1;
}
else
{
$continuedLine = 0;
}
if ( !defined $appendHere )
{
if ( $continuedLine == 1 )
{
# we will append continued lines to $lines[$appendHere]
$appendHere = $i;
}
}
else
{
chomp $lines[$appendHere]; # get rid of \n before appending next
chomp $lines[$i]; # get rid of \n before appending next
$lines[$appendHere] .= "$lines[$i]\n"; # append current line to previously marked location
$lines[$i] = "\n"; # leave only \n in the current line since we want to preserve line numbers
if ( $continuedLine == 0 ) # merge next line too?
{
$appendHere = undef;
}
}
}
#printFileFormatted();
######################## 4 - handle comments and strings ######################################
# similarly substituting a comment body with a single space may spoil our line numbers so
# we are just replacing comments with spaces preserving newlines where necessary
my $state = "out";
my $error;
my $COMMENT_SUBST = ' '; #'@';
my $STRING_SUBST = ' '; #'%';
ERROR: for ( my $line = 0; $line <= $#lines; $line++ )
{
state $hexVal = 0;
state $octVal = 0;
state $string = "";
my @chars = split //, $lines[$line];
my $newLine = "";
for ( my $i = 0; $i <= $#chars; $i++ )
{
my $c = $chars[$i];
if ( $state eq 'out' ) # ----------------------------------------------
{
if ( $c eq '/' )
{
$state = 'comment?';
$newLine .= $c;
}
elsif ( $c eq '"' )
{
$state = 'string char';
$newLine .= $STRING_SUBST;
}
else
{
$newLine .= $c;
}
}
elsif ( $state eq 'comment?' ) # ----------------------------------------------
{
if ( $c eq '/' )
{
$state = '//comment';
chop $newLine;
$newLine .= $COMMENT_SUBST x 2;
}
elsif ( $c eq '*' )
{
$state = '/*comment';
chop $newLine;
$newLine .= $COMMENT_SUBST x 2;
}
else
{
$state = 'out';
$newLine .= $c;
}
}
elsif ( $state eq '//comment' ) # ----------------------------------------------
{
if ( $c eq "\n" )
{
$state = 'out';
$newLine .= $c;
}
else
{
$newLine .= $COMMENT_SUBST;
}
}
elsif ( $state eq '/*comment' ) # ----------------------------------------------
{
if ( $c eq '*' )
{
$state = '/*comment end?';
$newLine .= $COMMENT_SUBST;
}
elsif ( $c eq "\n" )
{
$newLine .= $c;
}
else
{
$newLine .= $COMMENT_SUBST;
}
}
elsif ( $state eq '/*comment end?' ) # ----------------------------------------------
{
if ( $c eq '*' )
{
$newLine .= $COMMENT_SUBST;
}
elsif ( $c eq "\n" )
{
$newLine .= $c;
}
elsif ( $c eq '/' )
{
$state = 'out';
$newLine .= $COMMENT_SUBST;
}
else
{
$state = '/*comment';
$newLine .= $COMMENT_SUBST;
}
}
elsif ( $state eq 'string char' ) # ----------------------------------------------
{
# theoretically ignore "everything" within a string
# which may look like "abc\\" = abc\ or "abc\"" = abc"
# "abc\" - wrong - no end of string, "abc\\\" wrong again
# in order to detect if particular " terminates a string we have to check the whole string
# since it cannot be determined just by checking what the previous character was hence
# that state machine was created
if ( $c eq '"' )
{
$state = 'out';
$newLine .= $STRING_SUBST;
}
elsif ( $c eq "\\" )
{
$state = 'string esc seq';
$newLine .= $STRING_SUBST;
}
elsif ( $c eq "\n" )
{
$error = "line [".($line+1)."] - error - a newline within a string\n";
last ERROR;
}
else
{
$newLine .= $STRING_SUBST;
}
}
elsif ( $state eq 'string esc seq' ) # ----------------------------------------------
{
# simple esc seq \' \" \? \\ \a \b \f \n \r \t \v
# oct num \o \oo \ooo no more than 3 oct digits (o=[0-7]{1,3}) but value must be < than 255
# hex num \xh \xhh \xhhh..... unlimited number of hex digits (h=[0-9a-fA-F]+) but value must be < than 255
# in any other esc seq \ will be ignored hence \u=u \p=p \k=k etc
if ( $c =~ m#^['"\?\\abfhrtv]$# )
{
$state = 'string char';
$newLine .= $STRING_SUBST x 2;
}
elsif ( $c eq 'x' )
{
$state = 'string hex marker';
$newLine .= $STRING_SUBST;
}
elsif ( $c =~ m#^[0-7]$#)
{
$state = 'string oct';
$octVal = oct($c);
$newLine .= $STRING_SUBST;
}
elsif ( $c eq "\n" )
{
$error = "line [".($line+1)."] - error - a newline within a string\n";
last ERROR;
}
else # other esc seqences are ignored - usually a warning is issued
{
$state = 'string char';
$newLine .= $STRING_SUBST x 2;
}
}
elsif ( $state eq 'string hex marker' ) # ----------------------------------------------
{
if ( $c =~ m#^[0-9a-fA-F]$# )
{
$state = 'string hex';
$hexVal = hex($c);
$newLine .= $STRING_SUBST;
}
else
{
$error = "line [".($line+1)."] - error - hex escape sequence not finished\n";
last ERROR;
}
}
elsif ( $state eq 'string hex' ) # ----------------------------------------------
{
if ( $c =~ m#^[0-9a-fA-F]$# )
{
$hexVal <<= 4;
$hexVal += hex($c);
# treat as regular 8bit character sequence - no fancy long chars etc
if ( $hexVal > 255 )
{
$error = "line [".($line+1)."] - error - hex escape sequence too big for a character\n";
last ERROR;
}
$newLine .= $STRING_SUBST;
}
elsif ( $c eq '"' )
{
$state = 'out';
$newLine .= $STRING_SUBST;
$hexVal = 0;
}
elsif ( $c eq "\n" )
{
$error = "line [".($line+1)."] - error - a newline within a string\n";
last ERROR;
}
else
{
$state = 'string char';
$newLine .= $STRING_SUBST;
$hexVal = 0;
}
}
elsif ( $state eq 'string oct' ) # ----------------------------------------------
{
if ( $c =~ m#^[0-7]$# )
{
$octVal <<= 3;
$octVal += oct($c);
# treat as regular 8bit character sequence - no fancy long chars etc
if ( $octVal > 255 )
{
$error = "line [".($line+1)."] - error - oct esc sequence too big for a character\n";
last ERROR;
}
$newLine .= $STRING_SUBST;
}
elsif ( $c eq "\n" )
{
$error = "line [".($line+1)."] - error - a newline within a string\n";
last ERROR;
}
elsif ( $c eq '"' )
{
$state = 'out';
$newLine .= $STRING_SUBST;
$octVal = 0;
}
else
{
$state = 'string char';
$newLine .= $STRING_SUBST;
$octVal = 0;
}
}
else
{
$error = "line [".($line+1)."] - error - state machine problem - unknown state\n";
last ERROR;
}
}#for ( my $i = 0; $i <= $#chars; $i++ )
$lines[ $line ] = $newLine;
}#for ( my $line = 0; $line <= $#lines; $line++ )
if ( $error ) # errors detected within state machine?
{
print "$error";
exit(1);
}
else # EOF met - check the state
{
if ( $state eq 'out' )
{
# ok no problem
}
elsif ( $state eq 'comment?' )
{
# ok no problem - may be a division after all - not a preproc problem
}
elsif ( $state eq '//comment' )
{
# ok no problem
}
elsif ( $state eq '/*comment' )
{
print "EOF reached within /* */ comment\n";
exit(1);
}
elsif ( $state eq '/*comment end?' )
{
print "EOF reached within /* */ comment\n";
exit(1);
}
elsif ( $state eq 'string char' )
{
print "EOF reached within string\n";
exit(1);
}
elsif ( $state eq 'string esc seq' )
{
print "EOF reached within string\n";
exit(1);
}
elsif ( $state eq 'string hex marker' )
{
print "EOF reached within string\n";
exit(1);
}
elsif ( $state eq 'string hex' )
{
print "EOF reached within string\n";
exit(1);
}
elsif ( $state eq 'string oct' )
{
print "EOF reached within string\n";
exit(1);
}
else
{
print "EOF reached and state machine is in unknown state\n";
exit(1);
}
}
如果您正在编写标记器，并且您将包括检查字符串，因此您的模式不会匹配字符串内的注释，那么此模式将适用于您：
"(/[*][\S\s]*?[*]/)"