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csv.py15.8 KB · 449 lines
 """csv.py - read/write/investigate CSV files""" import refrom _csv import Error, __version__, writer, reader, register_dialect, \                 unregister_dialect, get_dialect, list_dialects, \                 field_size_limit, \                 QUOTE_MINIMAL, QUOTE_ALL, QUOTE_NONNUMERIC, QUOTE_NONE, \                 __doc__from _csv import Dialect as _Dialect from io import StringIO __all__ = ["QUOTE_MINIMAL", "QUOTE_ALL", "QUOTE_NONNUMERIC", "QUOTE_NONE",           "Error", "Dialect", "__doc__", "excel", "excel_tab",           "field_size_limit", "reader", "writer",           "register_dialect", "get_dialect", "list_dialects", "Sniffer",           "unregister_dialect", "__version__", "DictReader", "DictWriter",           "unix_dialect"] class Dialect:    """Describe a CSV dialect.     This must be subclassed (see csv.excel).  Valid attributes are:    delimiter, quotechar, escapechar, doublequote, skipinitialspace,    lineterminator, quoting.     """    _name = ""    _valid = False    # placeholders    delimiter = None    quotechar = None    escapechar = None    doublequote = None    skipinitialspace = None    lineterminator = None    quoting = None     def __init__(self):        if self.__class__ != Dialect:            self._valid = True        self._validate()     def _validate(self):        try:            _Dialect(self)        except TypeError as e:            # We do this for compatibility with py2.3            raise Error(str(e)) class excel(Dialect):    """Describe the usual properties of Excel-generated CSV files."""    delimiter = ','    quotechar = '"'    doublequote = True    skipinitialspace = False    lineterminator = '\r\n'    quoting = QUOTE_MINIMALregister_dialect("excel", excel) class excel_tab(excel):    """Describe the usual properties of Excel-generated TAB-delimited files."""    delimiter = '\t'register_dialect("excel-tab", excel_tab) class unix_dialect(Dialect):    """Describe the usual properties of Unix-generated CSV files."""    delimiter = ','    quotechar = '"'    doublequote = True    skipinitialspace = False    lineterminator = '\n'    quoting = QUOTE_ALLregister_dialect("unix", unix_dialect)  class DictReader:    def __init__(self, f, fieldnames=None, restkey=None, restval=None,                 dialect="excel", *args, **kwds):        self._fieldnames = fieldnames   # list of keys for the dict        self.restkey = restkey          # key to catch long rows        self.restval = restval          # default value for short rows        self.reader = reader(f, dialect, *args, **kwds)        self.dialect = dialect        self.line_num = 0     def __iter__(self):        return self     @property    def fieldnames(self):        if self._fieldnames is None:            try:                self._fieldnames = next(self.reader)            except StopIteration:                pass        self.line_num = self.reader.line_num        return self._fieldnames     @fieldnames.setter    def fieldnames(self, value):        self._fieldnames = value     def __next__(self):        if self.line_num == 0:            # Used only for its side effect.            self.fieldnames        row = next(self.reader)        self.line_num = self.reader.line_num         # unlike the basic reader, we prefer not to return blanks,        # because we will typically wind up with a dict full of None        # values        while row == []:            row = next(self.reader)        d = dict(zip(self.fieldnames, row))        lf = len(self.fieldnames)        lr = len(row)        if lf < lr:            d[self.restkey] = row[lf:]        elif lf > lr:            for key in self.fieldnames[lr:]:                d[key] = self.restval        return d  class DictWriter:    def __init__(self, f, fieldnames, restval="", extrasaction="raise",                 dialect="excel", *args, **kwds):        self.fieldnames = fieldnames    # list of keys for the dict        self.restval = restval          # for writing short dicts        if extrasaction.lower() not in ("raise", "ignore"):            raise ValueError("extrasaction (%s) must be 'raise' or 'ignore'"                             % extrasaction)        self.extrasaction = extrasaction        self.writer = writer(f, dialect, *args, **kwds)     def writeheader(self):        header = dict(zip(self.fieldnames, self.fieldnames))        return self.writerow(header)     def _dict_to_list(self, rowdict):        if self.extrasaction == "raise":            wrong_fields = rowdict.keys() - self.fieldnames            if wrong_fields:                raise ValueError("dict contains fields not in fieldnames: "                                 + ", ".join([repr(x) for x in wrong_fields]))        return (rowdict.get(key, self.restval) for key in self.fieldnames)     def writerow(self, rowdict):        return self.writer.writerow(self._dict_to_list(rowdict))     def writerows(self, rowdicts):        return self.writer.writerows(map(self._dict_to_list, rowdicts)) # Guard Sniffer's type checking against builds that exclude complex()try:    complexexcept NameError:    complex = float class Sniffer:    '''    "Sniffs" the format of a CSV file (i.e. delimiter, quotechar)    Returns a Dialect object.    '''    def __init__(self):        # in case there is more than one possible delimiter        self.preferred = [',', '\t', ';', ' ', ':']      def sniff(self, sample, delimiters=None):        """        Returns a dialect (or None) corresponding to the sample        """         quotechar, doublequote, delimiter, skipinitialspace = \                   self._guess_quote_and_delimiter(sample, delimiters)        if not delimiter:            delimiter, skipinitialspace = self._guess_delimiter(sample,                                                                delimiters)         if not delimiter:            raise Error("Could not determine delimiter")         class dialect(Dialect):            _name = "sniffed"            lineterminator = '\r\n'            quoting = QUOTE_MINIMAL            # escapechar = ''         dialect.doublequote = doublequote        dialect.delimiter = delimiter        # _csv.reader won't accept a quotechar of ''        dialect.quotechar = quotechar or '"'        dialect.skipinitialspace = skipinitialspace         return dialect      def _guess_quote_and_delimiter(self, data, delimiters):        """        Looks for text enclosed between two identical quotes        (the probable quotechar) which are preceded and followed        by the same character (the probable delimiter).        For example:                         ,'some text',        The quote with the most wins, same with the delimiter.        If there is no quotechar the delimiter can't be determined        this way.        """         matches = []        for restr in (r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?P=delim)', # ,".*?",                      r'(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?P<delim>[^\w\n"\'])(?P<space> ?)',   #  ".*?",                      r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?:$|\n)',   # ,".*?"                      r'(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?:$|\n)'):                            #  ".*?" (no delim, no space)            regexp = re.compile(restr, re.DOTALL | re.MULTILINE)            matches = regexp.findall(data)            if matches:                break         if not matches:            # (quotechar, doublequote, delimiter, skipinitialspace)            return ('', False, None, 0)        quotes = {}        delims = {}        spaces = 0        groupindex = regexp.groupindex        for m in matches:            n = groupindex['quote'] - 1            key = m[n]            if key:                quotes[key] = quotes.get(key, 0) + 1            try:                n = groupindex['delim'] - 1                key = m[n]            except KeyError:                continue            if key and (delimiters is None or key in delimiters):                delims[key] = delims.get(key, 0) + 1            try:                n = groupindex['space'] - 1            except KeyError:                continue            if m[n]:                spaces += 1         quotechar = max(quotes, key=quotes.get)         if delims:            delim = max(delims, key=delims.get)            skipinitialspace = delims[delim] == spaces            if delim == '\n': # most likely a file with a single column                delim = ''        else:            # there is *no* delimiter, it's a single column of quoted data            delim = ''            skipinitialspace = 0         # if we see an extra quote between delimiters, we've got a        # double quoted format        dq_regexp = re.compile(                               r"((%(delim)s)|^)\W*%(quote)s[^%(delim)s\n]*%(quote)s[^%(delim)s\n]*%(quote)s\W*((%(delim)s)|$)" % \                               {'delim':re.escape(delim), 'quote':quotechar}, re.MULTILINE)           if dq_regexp.search(data):            doublequote = True        else:            doublequote = False         return (quotechar, doublequote, delim, skipinitialspace)      def _guess_delimiter(self, data, delimiters):        """        The delimiter /should/ occur the same number of times on        each row. However, due to malformed data, it may not. We don't want        an all or nothing approach, so we allow for small variations in this        number.          1) build a table of the frequency of each character on every line.          2) build a table of frequencies of this frequency (meta-frequency?),             e.g.  'x occurred 5 times in 10 rows, 6 times in 1000 rows,             7 times in 2 rows'          3) use the mode of the meta-frequency to determine the /expected/             frequency for that character          4) find out how often the character actually meets that goal          5) the character that best meets its goal is the delimiter        For performance reasons, the data is evaluated in chunks, so it can        try and evaluate the smallest portion of the data possible, evaluating        additional chunks as necessary.        """         data = list(filter(None, data.split('\n')))         ascii = [chr(c) for c in range(127)] # 7-bit ASCII         # build frequency tables        chunkLength = min(10, len(data))        iteration = 0        charFrequency = {}        modes = {}        delims = {}        start, end = 0, chunkLength        while start < len(data):            iteration += 1            for line in data[start:end]:                for char in ascii:                    metaFrequency = charFrequency.get(char, {})                    # must count even if frequency is 0                    freq = line.count(char)                    # value is the mode                    metaFrequency[freq] = metaFrequency.get(freq, 0) + 1                    charFrequency[char] = metaFrequency             for char in charFrequency.keys():                items = list(charFrequency[char].items())                if len(items) == 1 and items[0][0] == 0:                    continue                # get the mode of the frequencies                if len(items) > 1:                    modes[char] = max(items, key=lambda x: x[1])                    # adjust the mode - subtract the sum of all                    # other frequencies                    items.remove(modes[char])                    modes[char] = (modes[char][0], modes[char][1]                                   - sum(item[1] for item in items))                else:                    modes[char] = items[0]             # build a list of possible delimiters            modeList = modes.items()            total = float(min(chunkLength * iteration, len(data)))            # (rows of consistent data) / (number of rows) = 100%            consistency = 1.0            # minimum consistency threshold            threshold = 0.9            while len(delims) == 0 and consistency >= threshold:                for k, v in modeList:                    if v[0] > 0 and v[1] > 0:                        if ((v[1]/total) >= consistency and                            (delimiters is None or k in delimiters)):                            delims[k] = v                consistency -= 0.01             if len(delims) == 1:                delim = list(delims.keys())[0]                skipinitialspace = (data[0].count(delim) ==                                    data[0].count("%c " % delim))                return (delim, skipinitialspace)             # analyze another chunkLength lines            start = end            end += chunkLength         if not delims:            return ('', 0)         # if there's more than one, fall back to a 'preferred' list        if len(delims) > 1:            for d in self.preferred:                if d in delims.keys():                    skipinitialspace = (data[0].count(d) ==                                        data[0].count("%c " % d))                    return (d, skipinitialspace)         # nothing else indicates a preference, pick the character that        # dominates(?)        items = [(v,k) for (k,v) in delims.items()]        items.sort()        delim = items[-1][1]         skipinitialspace = (data[0].count(delim) ==                            data[0].count("%c " % delim))        return (delim, skipinitialspace)      def has_header(self, sample):        # Creates a dictionary of types of data in each column. If any        # column is of a single type (say, integers), *except* for the first        # row, then the first row is presumed to be labels. If the type        # can't be determined, it is assumed to be a string in which case        # the length of the string is the determining factor: if all of the        # rows except for the first are the same length, it's a header.        # Finally, a 'vote' is taken at the end for each column, adding or        # subtracting from the likelihood of the first row being a header.         rdr = reader(StringIO(sample), self.sniff(sample))         header = next(rdr) # assume first row is header         columns = len(header)        columnTypes = {}        for i in range(columns): columnTypes[i] = None         checked = 0        for row in rdr:            # arbitrary number of rows to check, to keep it sane            if checked > 20:                break            checked += 1             if len(row) != columns:                continue # skip rows that have irregular number of columns             for col in list(columnTypes.keys()):                 for thisType in [int, float, complex]:                    try:                        thisType(row[col])                        break                    except (ValueError, OverflowError):                        pass                else:                    # fallback to length of string                    thisType = len(row[col])                 if thisType != columnTypes[col]:                    if columnTypes[col] is None: # add new column type                        columnTypes[col] = thisType                    else:                        # type is inconsistent, remove column from                        # consideration                        del columnTypes[col]         # finally, compare results against first row and "vote"        # on whether it's a header        hasHeader = 0        for col, colType in columnTypes.items():            if type(colType) == type(0): # it's a length                if len(header[col]) != colType:                    hasHeader += 1                else:                    hasHeader -= 1            else: # attempt typecast                try:                    colType(header[col])                except (ValueError, TypeError):                    hasHeader += 1                else:                    hasHeader -= 1         return hasHeader > 0