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