is the main function in python is exact compare to Java main method?
all execution start in main which may takes arguments?
like the follow example script -
def main(argv):
==============================
and what is
__name__
__main__
use for in terms of Java?
thanks
==============================
#!/usr/bin/env python
"""
Preprocess a file.
Command Line Usage:
preprocess [<options>...] <infile>
Options:
-h, --help Print this help and exit.
-v, --verbose Give verbose output for errors.
-o <outfile> Write output to the given file instead of to
stdout.
-D <define> Define a variable for preprocessing. <define>
can simply be a variable name (in which case
it
will be true) or it can be of the form
<var>=<val>. An attempt will be made to
convert
<val> to an integer so "-D FOO=0" will create
a
false value.
Module Usage:
from preprocess import preprocess
preprocess(infile, outfile=sys.stdout, defines={})
The <infile> can be marked up with special preprocessor statement
lines
of the form:
<comment-prefix> <preprocessor-stmt> <comment-suffix>
where the <comment-prefix/suffix> are the native comment
delimiters for
that file type. Examples:
<!-- #if FOO -->
...
<!-- #endif -->
# #if defined('FAV_COLOR') and FAV_COLOR == "blue"
...
# #elif FAV_COLOR == "red"
...
# #else
...
# #endif
Preprocessor Syntax:
- Valid statements:
#define <var>[=<value>]
#undef <var>
#if <expr>
#elif <expr>
#else
#endif
#error <error string>
where <expr> is any valid Python expression.
- The expression after #if/elif may be a Python statement. It
is an
error to refer to a variable that has not been defined by a
-D
option.
- Special built-in methods for expressions:
defined(varName) Return true if given variable is
defined.
"""
import os
import sys
import getopt
import types
import re
import pprint
import logging
from contenttype import getContentType
#---- exceptions
class PreprocessError(Exception):
def __init__(self, errmsg, file=None, lineno=None, line=None):
self.errmsg = str(errmsg)
self.file = file
self.lineno = lineno
self.line = line
Exception.__init__(self, errmsg, file, lineno, line)
def __str__(self):
s = ""
if self.file is not None:
s += self.file + ":"
if self.lineno is not None:
s += str(self.lineno) + ":"
if self.file is not None or self.lineno is not None:
s += " "
s += self.errmsg
return s
#---- global data
log = logging.getLogger("preprocess")
# Comment delimiter info.
# A mapping of content type to a list of 2-tuples defining the line
# prefix and suffix for a comment.
_commentGroups = {
"Python": [ ('#', '') ],
"Perl": [ ('#', '') ],
"Tcl": [ ('#', '') ],
"XML": [ ('<!--', '-->') ],
"HTML": [ ('<!--', '-->') ],
"Makefile": [ ('#', '') ],
"JavaScript": [ ('/*', '*/'), ('//', '') ],
"CSS": [ ('/*', '*/') ],
"C": [ ('/*', '*/') ],
"C++": [ ('/*', '*/'), ('//', '') ],
"IDL": [ ('/*', '*/'), ('//', '') ],
"Text": [ ('#', '') ],
}
#---- internal support stuff
def _evaluate(expr, defines):
"""Evaluate the given expression string with the given context."""
try:
rv = eval(expr, {'defined':lambda v: v in defines}, defines)
except Exception, ex:
raise PreprocessError(str(ex), defines['__FILE__'],
defines['__LINE__'])
log.debug("evaluate %r -> %s (defines=%r)", expr, rv, defines)
return rv
#---- module API
def preprocess(infile, outfile=sys.stdout, defines={}):
"""Preprocess the given file.
"infile" is the input filename.
"outfile" is the output filename or stream (default is
sys.stdout).
"defines" is a dictionary of defined variables that will be
understood in preprocessor statements. Keys must be strings
and,
currently, only the truth value of any key's value matters.
Returns the modified dictionary of defines or raises
PreprocessError if
there was some problem.
"""
log.info("preprocess(infile=%r, outfile=%r, defines=%r)",
infile, outfile, defines)
# Determine the content type and comment info for the input file.
contentType = getContentType(infile)
if contentType is None:
contentType = "Text"
log.warn("defaulting content type for '%s' to '%s'",
infile, contentType)
try:
cgs = _commentGroups[contentType]
except KeyError:
raise PreprocessError("don't know comment delimiters for
content "\
"type '%s' (file '%s')"\
% (contentType, infile))
# Generate statement parsing regexes.
stmts = ['#\s*(?P<op>if|elif|ifdef|ifndef)\s+(?P<expr>.*?)',
'#\s*(?P<op>else|endif)',
'#\s*(?P<op>error)\s+(?P<error>.*?)',
'#\s*(?P<op>define)\s+(?P<var>[^\s]*?)(\s+(?P<val>.+?))?',
'#\s*(?P<op>undef)\s+(?P<var>[^\s]*?)']
patterns = ['^\s*%s\s*%s\s*%s\s*$'
% (re.escape(cg[0]), stmt, re.escape(cg[1]))
for cg in cgs for stmt in stmts]
stmtRes = [re.compile(p) for p in patterns]
# Process the input file.
fin = open(infile, 'r')
if type(outfile) in types.StringTypes:
if os.path.exists(outfile):
os.chmod(outfile, 0777)
os.remove(outfile)
fout = open(outfile, 'w')
else:
fout = outfile
defines['__FILE__'] = infile
SKIP, EMIT = range(2) # states
states = [(EMIT, # a state is
(<emit-or-skip-lines-in-this-section>,
0, # <have-emitted-in-this-if-block>,
0)] # <have-seen-'else'-in-this-if-block>)
lineNum = 0
for line in fin.readlines():
lineNum += 1
log.debug("line %d: %r", lineNum, line)
defines['__LINE__'] = lineNum
# Is this line a preprocessor stmt line?
for stmtRe in stmtRes:
match = stmtRe.match(line)
if match:
break
else:
match = None
if match:
op = match.group("op")
log.debug("%r stmt (states: %r)", op, states)
if op == "define":
if states and states[-1][0] == SKIP: continue
var, val = match.group("var", "val")
if val is None:
val = None
else:
try:
val = eval(val, {}, {})
except:
pass
defines[var] = val
elif op == "undef":
if states and states[-1][0] == SKIP: continue
var = match.group("var")
try:
del defines[var]
except KeyError:
pass
elif op in ("if", "ifdef", "ifndef"):
if op == "if":
expr = match.group("expr")
elif op == "ifdef":
expr = "defined('%s')" % match.group("expr")
elif op == "ifndef":
expr = "not defined('%s')" % match.group("expr")
try:
if states and states[-1][0] == SKIP:
# Were are nested in a SKIP-portion of an
if-block.
states.append((SKIP, 0, 0))
elif _evaluate(expr, defines):
states.append((EMIT, 1, 0))
else:
states.append((SKIP, 0, 0))
except KeyError:
raise PreprocessError("use of undefined variable
in "\
"#%s stmt" % op,
defines['__FILE__'],
defines['__LINE__'], line)
elif op == "elif":
expr = match.group("expr")
try:
if states[-1][2]: # already had #else in this
if-block
raise PreprocessError("illegal #elif after
#else in "\
"same #if block", defines['__FILE__'],
defines['__LINE__'], line)
elif states[-1][1]: # if have emitted in this
if-block
states[-1] = (SKIP, 1, 0)
elif states[:-1] and states[-2][0] == SKIP:
# Were are nested in a SKIP-portion of an
if-block.
states[-1] = (SKIP, 0, 0)
elif _evaluate(expr, defines):
states[-1] = (EMIT, 1, 0)
else:
states[-1] = (SKIP, 0, 0)
except IndexError:
raise PreprocessError("#elif stmt without leading
#if "\
"stmt", defines['__FILE__'],
defines['__LINE__'], line)
elif op == "else":
try:
if states[-1][2]: # already had #else in this
if-block
raise PreprocessError("illegal #else after
#else in "\
"same #if block", defines['__FILE__'],
defines['__LINE__'], line)
elif states[-1][1]: # if have emitted in this
if-block
states[-1] = (SKIP, 1, 1)
elif states[:-1] and states[-2][0] == SKIP:
# Were are nested in a SKIP-portion of an
if-block.
states[-1] = (SKIP, 0, 1)
else:
states[-1] = (EMIT, 1, 1)
except IndexError:
raise PreprocessError("#else stmt without leading
#if "\
"stmt", defines['__FILE__'],
defines['__LINE__'], line)
elif op == "endif":
try:
states.pop()
except IndexError:
raise PreprocessError("#endif stmt without leading
#if"\
"stmt", defines['__FILE__'],
defines['__LINE__'], line)
elif op == "error":
if states and states[-1][0] == SKIP: continue
error = match.group("error")
raise PreprocessError("#error: "+error,
defines['__FILE__'],
defines['__LINE__'], line)
log.debug("states: %r", states)
else:
try:
if states[-1][0] == EMIT:
log.debug("emit line (%s)" % states[-1][1])
fout.write(line)
else:
log.debug("skip line (%s)" % states[-1][1])
except IndexError:
raise PreprocessError("superfluous #endif before this
line",
defines['__FILE__'],
defines['__LINE__'])
if len(states) > 1:
raise PreprocessError("unterminated #if block",
defines['__FILE__'],
defines['__LINE__'])
elif len(states) < 1:
raise PreprocessError("superfluous #endif on or before this
line",
defines['__FILE__'],
defines['__LINE__'])
if fout != outfile:
fout.close()
#---- mainline
def main(argv):
try:
optlist, args = getopt.getopt(argv[1:], 'hvo:D:', ['help',
'verbose'])
except getopt.GetoptError, msg:
sys.stderr.write("preprocess: error: %s" % msg)
sys.stderr.write("See 'preprocess --help'.\n")
return 1
outfile = sys.stdout
defines = {}
for opt, optarg in optlist:
if opt in ('-h', '--help'):
sys.stdout.write(__doc__)
return 0
elif opt in ('-v', '--verbose'):
log.setLevel(logging.DEBUG)
elif opt == '-o':
outfile = optarg
elif opt == '-D':
if optarg.find('=') != -1:
var, val = optarg.split('=', 1)
try:
val = eval(val, {}, {})
except:
pass
else:
var, val = optarg, None
defines[var] = val
if len(args) != 1:
sys.stderr.write("preprocess: error: incorrect number of "\
"arguments: argv=%r\n" % argv)
return 1
else:
infile = args[0]
try:
preprocess(infile, outfile, defines)
except PreprocessError, ex:
sys.stderr.write("preprocess: error: %s\n" % str(ex))
if __name__ == "__main__":
sys.exit( main(sys.argv) )
--
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