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| """text_file | |
| provides the TextFile class, which gives an interface to text files | |
| that (optionally) takes care of stripping comments, ignoring blank | |
| lines, and joining lines with backslashes.""" | |
| import sys, io | |
| class TextFile: | |
| """Provides a file-like object that takes care of all the things you | |
| commonly want to do when processing a text file that has some | |
| line-by-line syntax: strip comments (as long as "#" is your | |
| comment character), skip blank lines, join adjacent lines by | |
| escaping the newline (ie. backslash at end of line), strip | |
| leading and/or trailing whitespace. All of these are optional | |
| and independently controllable. | |
| Provides a 'warn()' method so you can generate warning messages that | |
| report physical line number, even if the logical line in question | |
| spans multiple physical lines. Also provides 'unreadline()' for | |
| implementing line-at-a-time lookahead. | |
| Constructor is called as: | |
| TextFile (filename=None, file=None, **options) | |
| It bombs (RuntimeError) if both 'filename' and 'file' are None; | |
| 'filename' should be a string, and 'file' a file object (or | |
| something that provides 'readline()' and 'close()' methods). It is | |
| recommended that you supply at least 'filename', so that TextFile | |
| can include it in warning messages. If 'file' is not supplied, | |
| TextFile creates its own using 'io.open()'. | |
| The options are all boolean, and affect the value returned by | |
| 'readline()': | |
| strip_comments [default: true] | |
| strip from "#" to end-of-line, as well as any whitespace | |
| leading up to the "#" -- unless it is escaped by a backslash | |
| lstrip_ws [default: false] | |
| strip leading whitespace from each line before returning it | |
| rstrip_ws [default: true] | |
| strip trailing whitespace (including line terminator!) from | |
| each line before returning it | |
| skip_blanks [default: true} | |
| skip lines that are empty *after* stripping comments and | |
| whitespace. (If both lstrip_ws and rstrip_ws are false, | |
| then some lines may consist of solely whitespace: these will | |
| *not* be skipped, even if 'skip_blanks' is true.) | |
| join_lines [default: false] | |
| if a backslash is the last non-newline character on a line | |
| after stripping comments and whitespace, join the following line | |
| to it to form one "logical line"; if N consecutive lines end | |
| with a backslash, then N+1 physical lines will be joined to | |
| form one logical line. | |
| collapse_join [default: false] | |
| strip leading whitespace from lines that are joined to their | |
| predecessor; only matters if (join_lines and not lstrip_ws) | |
| errors [default: 'strict'] | |
| error handler used to decode the file content | |
| Note that since 'rstrip_ws' can strip the trailing newline, the | |
| semantics of 'readline()' must differ from those of the builtin file | |
| object's 'readline()' method! In particular, 'readline()' returns | |
| None for end-of-file: an empty string might just be a blank line (or | |
| an all-whitespace line), if 'rstrip_ws' is true but 'skip_blanks' is | |
| not.""" | |
| default_options = { 'strip_comments': 1, | |
| 'skip_blanks': 1, | |
| 'lstrip_ws': 0, | |
| 'rstrip_ws': 1, | |
| 'join_lines': 0, | |
| 'collapse_join': 0, | |
| 'errors': 'strict', | |
| } | |
| def __init__(self, filename=None, file=None, **options): | |
| """Construct a new TextFile object. At least one of 'filename' | |
| (a string) and 'file' (a file-like object) must be supplied. | |
| They keyword argument options are described above and affect | |
| the values returned by 'readline()'.""" | |
| if filename is None and file is None: | |
| raise RuntimeError("you must supply either or both of 'filename' and 'file'") | |
| # set values for all options -- either from client option hash | |
| # or fallback to default_options | |
| for opt in self.default_options.keys(): | |
| if opt in options: | |
| setattr(self, opt, options[opt]) | |
| else: | |
| setattr(self, opt, self.default_options[opt]) | |
| # sanity check client option hash | |
| for opt in options.keys(): | |
| if opt not in self.default_options: | |
| raise KeyError("invalid TextFile option '%s'" % opt) | |
| if file is None: | |
| self.open(filename) | |
| else: | |
| self.filename = filename | |
| self.file = file | |
| self.current_line = 0 # assuming that file is at BOF! | |
| # 'linebuf' is a stack of lines that will be emptied before we | |
| # actually read from the file; it's only populated by an | |
| # 'unreadline()' operation | |
| self.linebuf = [] | |
| def open(self, filename): | |
| """Open a new file named 'filename'. This overrides both the | |
| 'filename' and 'file' arguments to the constructor.""" | |
| self.filename = filename | |
| self.file = io.open(self.filename, 'r', errors=self.errors) | |
| self.current_line = 0 | |
| def close(self): | |
| """Close the current file and forget everything we know about it | |
| (filename, current line number).""" | |
| file = self.file | |
| self.file = None | |
| self.filename = None | |
| self.current_line = None | |
| file.close() | |
| def gen_error(self, msg, line=None): | |
| outmsg = [] | |
| if line is None: | |
| line = self.current_line | |
| outmsg.append(self.filename + ", ") | |
| if isinstance(line, (list, tuple)): | |
| outmsg.append("lines %d-%d: " % tuple(line)) | |
| else: | |
| outmsg.append("line %d: " % line) | |
| outmsg.append(str(msg)) | |
| return "".join(outmsg) | |
| def error(self, msg, line=None): | |
| raise ValueError("error: " + self.gen_error(msg, line)) | |
| def warn(self, msg, line=None): | |
| """Print (to stderr) a warning message tied to the current logical | |
| line in the current file. If the current logical line in the | |
| file spans multiple physical lines, the warning refers to the | |
| whole range, eg. "lines 3-5". If 'line' supplied, it overrides | |
| the current line number; it may be a list or tuple to indicate a | |
| range of physical lines, or an integer for a single physical | |
| line.""" | |
| sys.stderr.write("warning: " + self.gen_error(msg, line) + "\n") | |
| def readline(self): | |
| """Read and return a single logical line from the current file (or | |
| from an internal buffer if lines have previously been "unread" | |
| with 'unreadline()'). If the 'join_lines' option is true, this | |
| may involve reading multiple physical lines concatenated into a | |
| single string. Updates the current line number, so calling | |
| 'warn()' after 'readline()' emits a warning about the physical | |
| line(s) just read. Returns None on end-of-file, since the empty | |
| string can occur if 'rstrip_ws' is true but 'strip_blanks' is | |
| not.""" | |
| # If any "unread" lines waiting in 'linebuf', return the top | |
| # one. (We don't actually buffer read-ahead data -- lines only | |
| # get put in 'linebuf' if the client explicitly does an | |
| # 'unreadline()'. | |
| if self.linebuf: | |
| line = self.linebuf[-1] | |
| del self.linebuf[-1] | |
| return line | |
| buildup_line = '' | |
| while True: | |
| # read the line, make it None if EOF | |
| line = self.file.readline() | |
| if line == '': | |
| line = None | |
| if self.strip_comments and line: | |
| # Look for the first "#" in the line. If none, never | |
| # mind. If we find one and it's the first character, or | |
| # is not preceded by "\", then it starts a comment -- | |
| # strip the comment, strip whitespace before it, and | |
| # carry on. Otherwise, it's just an escaped "#", so | |
| # unescape it (and any other escaped "#"'s that might be | |
| # lurking in there) and otherwise leave the line alone. | |
| pos = line.find("#") | |
| if pos == -1: # no "#" -- no comments | |
| pass | |
| # It's definitely a comment -- either "#" is the first | |
| # character, or it's elsewhere and unescaped. | |
| elif pos == 0 or line[pos-1] != "\\": | |
| # Have to preserve the trailing newline, because it's | |
| # the job of a later step (rstrip_ws) to remove it -- | |
| # and if rstrip_ws is false, we'd better preserve it! | |
| # (NB. this means that if the final line is all comment | |
| # and has no trailing newline, we will think that it's | |
| # EOF; I think that's OK.) | |
| eol = (line[-1] == '\n') and '\n' or '' | |
| line = line[0:pos] + eol | |
| # If all that's left is whitespace, then skip line | |
| # *now*, before we try to join it to 'buildup_line' -- | |
| # that way constructs like | |
| # hello \\ | |
| # # comment that should be ignored | |
| # there | |
| # result in "hello there". | |
| if line.strip() == "": | |
| continue | |
| else: # it's an escaped "#" | |
| line = line.replace("\\#", "#") | |
| # did previous line end with a backslash? then accumulate | |
| if self.join_lines and buildup_line: | |
| # oops: end of file | |
| if line is None: | |
| self.warn("continuation line immediately precedes " | |
| "end-of-file") | |
| return buildup_line | |
| if self.collapse_join: | |
| line = line.lstrip() | |
| line = buildup_line + line | |
| # careful: pay attention to line number when incrementing it | |
| if isinstance(self.current_line, list): | |
| self.current_line[1] = self.current_line[1] + 1 | |
| else: | |
| self.current_line = [self.current_line, | |
| self.current_line + 1] | |
| # just an ordinary line, read it as usual | |
| else: | |
| if line is None: # eof | |
| return None | |
| # still have to be careful about incrementing the line number! | |
| if isinstance(self.current_line, list): | |
| self.current_line = self.current_line[1] + 1 | |
| else: | |
| self.current_line = self.current_line + 1 | |
| # strip whitespace however the client wants (leading and | |
| # trailing, or one or the other, or neither) | |
| if self.lstrip_ws and self.rstrip_ws: | |
| line = line.strip() | |
| elif self.lstrip_ws: | |
| line = line.lstrip() | |
| elif self.rstrip_ws: | |
| line = line.rstrip() | |
| # blank line (whether we rstrip'ed or not)? skip to next line | |
| # if appropriate | |
| if (line == '' or line == '\n') and self.skip_blanks: | |
| continue | |
| if self.join_lines: | |
| if line[-1] == '\\': | |
| buildup_line = line[:-1] | |
| continue | |
| if line[-2:] == '\\\n': | |
| buildup_line = line[0:-2] + '\n' | |
| continue | |
| # well, I guess there's some actual content there: return it | |
| return line | |
| def readlines(self): | |
| """Read and return the list of all logical lines remaining in the | |
| current file.""" | |
| lines = [] | |
| while True: | |
| line = self.readline() | |
| if line is None: | |
| return lines | |
| lines.append(line) | |
| def unreadline(self, line): | |
| """Push 'line' (a string) onto an internal buffer that will be | |
| checked by future 'readline()' calls. Handy for implementing | |
| a parser with line-at-a-time lookahead.""" | |
| self.linebuf.append(line) | |