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# CSV I/O
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import csv
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import _csv
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import StringIO
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import strings
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import util
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delims = ',;\t|`'
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tab_padded_delims = ['\t|\t']
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tsv_delim = '\t'
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escape = '\\'
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ending_placeholder = r'\n'
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def is_tsv(dialect): return dialect.delimiter.startswith(tsv_delim)
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def sniff(line):
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'''Automatically detects the dialect'''
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line, ending = strings.extract_line_ending(line)
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dialect = csv.Sniffer().sniff(line, delims)
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if is_tsv(dialect):
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# TSVs usually don't quote fields (nor doublequote embedded quotes)
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dialect.quoting = csv.QUOTE_NONE
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# Check multi-char delims using \t
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delim = strings.find_any(line, tab_padded_delims)
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if delim:
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dialect.delimiter = delim
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line_suffix = delim.rstrip('\t')
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if line.endswith(line_suffix): ending = line_suffix+ending
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else: dialect.doublequote = True # Sniffer doesn't turn this on by default
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dialect.lineterminator = ending
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return dialect
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def stream_info(stream, parse_header=False):
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'''Automatically detects the dialect based on the header line
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@return NamedTuple {header_line, header, dialect}'''
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info = util.NamedTuple()
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info.header_line = stream.readline()
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info.header = None
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if info.header_line != '':
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info.dialect = sniff(info.header_line)
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if parse_header:
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info.header = reader_class(info.dialect)(
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StringIO.StringIO(info.header_line), info.dialect).next()
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else: info.dialect = None # line of '' indicates EOF = empty stream
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return info
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tsv_encode_map = strings.json_encode_map[:]
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tsv_encode_map.append(('\t', r'\t'))
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tsv_decode_map = strings.flip_map(tsv_encode_map)
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class TsvReader:
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'''Unlike csv.reader, for TSVs, interprets \ as escaping a line ending but
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ignores it before everything else (e.g. \N for NULL).
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Also expands tsv_encode_map escapes.
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'''
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def __init__(self, stream, dialect):
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assert is_tsv(dialect)
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self.stream = stream
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self.dialect = dialect
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def __iter__(self): return self
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def next(self):
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record = ''
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ending = None
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while True:
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line = self.stream.readline()
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if line == '': raise StopIteration
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line = strings.remove_suffix(self.dialect.lineterminator, line)
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contents = strings.remove_suffix(escape, line)
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record += contents
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if len(contents) == len(line): break # no line continuation
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record += ending_placeholder
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# Prevent "new-line character seen in unquoted field" errors
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record = record.replace('\r', ending_placeholder)
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row = record.split(self.dialect.delimiter)
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return [strings.replace_all(tsv_decode_map, v) for v in row]
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def reader_class(dialect):
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if is_tsv(dialect): return TsvReader
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else: return csv.reader
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def make_reader(stream, dialect): return reader_class(dialect)(stream, dialect)
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def reader_and_header(stream):
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'''Automatically detects the dialect based on the header line
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@return tuple (reader, header)'''
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info = stream_info(stream, parse_header=True)
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return (make_reader(stream, info.dialect), info.header)
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##### csv modifications
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# Note that these methods only work on *instances* of Dialect classes
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csv.Dialect.__eq__ = lambda self, other: self.__dict__ == other.__dict__
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csv.Dialect.__ne__ = lambda self, other: not (self == other)
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__Dialect__validate_orig = csv.Dialect._validate
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def __Dialect__validate(self):
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try: __Dialect__validate_orig(self)
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except _csv.Error, e:
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if str(e) == '"delimiter" must be an 1-character string': pass # OK
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else: raise
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csv.Dialect._validate = __Dialect__validate
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##### Row filters
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class Filter:
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'''Wraps a reader, filtering each row'''
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def __init__(self, filter_, reader):
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self.reader = reader
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self.filter = filter_
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def __iter__(self): return self
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def next(self): return self.filter(self.reader.next())
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std_nulls = [r'\N']
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empty_nulls = [''] + std_nulls
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class NullFilter(Filter):
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'''Translates special string values to None'''
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def __init__(self, reader, nulls=std_nulls):
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map_ = dict.fromkeys(nulls, None)
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def filter_(row): return [map_.get(v, v) for v in row]
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Filter.__init__(self, filter_, reader)
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class StripFilter(Filter):
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'''Strips whitespace'''
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def __init__(self, reader):
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def filter_(row): return [v.strip() for v in row]
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Filter.__init__(self, filter_, reader)
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class ColCtFilter(Filter):
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'''Gives all rows the same # columns'''
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def __init__(self, reader, cols_ct):
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def filter_(row): return util.list_as_length(row, cols_ct)
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Filter.__init__(self, filter_, reader)
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##### Translators
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class InputRewriter:
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'''Wraps a reader, writing each row back to CSV'''
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def __init__(self, reader, dialect=csv.excel):
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self.reader = reader
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self.dialect = dialect
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def readline(self):
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try: row = self.reader.next()
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except StopIteration: return '' # EOF
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line_stream = StringIO.StringIO()
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csv.writer(line_stream, self.dialect).writerow(row)
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return line_stream.getvalue()
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def read(self, n): return self.readline() # forward all reads to readline()
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