# CSV I/O

import csv

escape = '\\'

    '''Automatically detects the dialect'''

        # TSVs usually don't quote fields (nor doublequote embedded quotes)

        dialect.quoting = csv.QUOTE_NONE

        # Check multi-char delims using \t

        delim = strings.find_any(line, tab_padded_delims)

        if delim:

            dialect.delimiter = delim

            line_suffix = delim.rstrip('\t')

            if line.endswith(line_suffix): ending = line_suffix+ending

    Uses the Excel dialect if the CSV file is empty.

    info.header_line = stream.readline()

    if info.header_line != '':

        info.dialect = sniff(info.header_line)

    if parse_header:

        try: info.header = reader_class(info.dialect)(

            StringIO.StringIO(info.header_line), info.dialect).next()

        except StopIteration: info.header = []

tsv_encode_map.append(('\t', r'\t'))

tsv_decode_map = strings.flip_map(tsv_encode_map)

    '''Unlike csv.reader, for TSVs, interprets \ as escaping a line ending but

        assert is_tsv(dialect)

        self.stream = stream

        self.dialect = dialect

    def __iter__(self): return self

    def next(self):

        record = ''

        ending = None

        while True:

            line = self.stream.readline()

            if line == '': raise StopIteration

        # Prevent "new-line character seen in unquoted field" errors

        record = record.replace('\r', ending_placeholder)

def reader_class(dialect):

    if is_tsv(dialect): return TsvReader

    else: return csv.reader

def make_reader(stream, dialect): return reader_class(dialect)(stream, dialect)

    '''Automatically detects the dialect based on the header line

    @return tuple (reader, header)'''

##### csv modifications

# Note that these methods only work on *instances* of Dialect classes

csv.Dialect.__eq__ = lambda self, other: self.__dict__ == other.__dict__

csv.Dialect.__ne__ = lambda self, other: not (self == other)

def __Dialect__validate(self):

        try: __Dialect__validate_orig(self)

        except _csv.Error, e:

            if str(e) == '"delimiter" must be an 1-character string': pass # OK

            else: raise

csv.Dialect._validate = __Dialect__validate

class Filter:

    '''Wraps a reader, filtering each row'''

    def __init__(self, filter_, reader):

        self.reader = reader

        self.filter = filter_

    def __iter__(self): return self

    def next(self): return self.filter(self.reader.next())

    def close(self): pass # support using as a stream

std_nulls = [r'\N']

empty_nulls = [''] + std_nulls

class NullFilter(Filter):

    '''Translates special string values to None'''

    def __init__(self, reader, nulls=std_nulls):

        map_ = dict.fromkeys(nulls, None)

        def filter_(row): return [map_.get(v, v) for v in row]

        Filter.__init__(self, filter_, reader)

class StripFilter(Filter):

    '''Strips whitespace'''

    def __init__(self, reader):

        def filter_(row): return [v.strip() for v in row]

        Filter.__init__(self, filter_, reader)

class ColCtFilter(Filter):

    '''Gives all rows the same # columns'''

    def __init__(self, reader, cols_ct):

        def filter_(row): return util.list_as_length(row, cols_ct)

        Filter.__init__(self, filter_, reader)

##### Translators

    '''Wraps a reader in a way that's usable to a filter stream that does not

    require lines to be strings. Reports EOF as '' instead of StopIteration.'''

    def __init__(self, reader):

        Filter.__init__(self, None, reader)

    def readline(self):

        try: return self.reader.next()

        except StopIteration: return '' # EOF

    '''Adds a column to each row

    @param mk_value(row, row_num)

    '''

    def __init__(self, reader, mk_value, index=0):

        def filter_(row):

            row = list(row) # make sure it's mutable; don't modify input!

            row.insert(index, mk_value(row, self.reader.line_num))

            return row

        Filter.__init__(self, filter_,

            streams.LineCountInputStream(StreamFilter(reader)))

    def __init__(self, reader):

        ColInsertFilter.__init__(self, reader, mk_value, 0)

    def __init__(self, reader, dialect=csv.excel):

    def readline(self):

        csv.writer(line_stream, self.dialect).writerow(row)

        return line_stream.getvalue()

    def read(self, n): return self.readline() # forward all reads to readline()