1
|
# CSV I/O
|
2
|
|
3
|
import csv
|
4
|
import StringIO
|
5
|
|
6
|
import strings
|
7
|
import util
|
8
|
|
9
|
delims = ',;\t`'
|
10
|
tsv_delim = '\t'
|
11
|
escape = '\\'
|
12
|
|
13
|
ending_placeholder = r'\n'
|
14
|
|
15
|
def is_tsv(dialect): return dialect.delimiter == tsv_delim
|
16
|
|
17
|
def sniff(line):
|
18
|
'''Automatically detects the dialect'''
|
19
|
dialect = csv.Sniffer().sniff(line, delims)
|
20
|
# TSVs usually don't quote fields (nor doublequote embedded quotes)
|
21
|
if is_tsv(dialect): dialect.quoting = csv.QUOTE_NONE
|
22
|
else: dialect.doublequote = True # Sniffer doesn't turn this on by default
|
23
|
return dialect
|
24
|
|
25
|
def stream_info(stream, parse_header=False):
|
26
|
'''Automatically detects the dialect based on the header line
|
27
|
@return NamedTuple {header_line, header, dialect}'''
|
28
|
info = util.NamedTuple()
|
29
|
info.header_line = stream.readline()
|
30
|
info.header = None
|
31
|
if info.header_line != '':
|
32
|
info.dialect = sniff(info.header_line)
|
33
|
if parse_header:
|
34
|
info.header = reader_class(info.dialect)(
|
35
|
StringIO.StringIO(info.header_line), info.dialect).next()
|
36
|
else: info.dialect = None # line of '' indicates EOF = empty stream
|
37
|
return info
|
38
|
|
39
|
class TsvReader:
|
40
|
'''Unlike csv.reader, for TSVs, interprets \ as escaping a line ending but
|
41
|
ignores it before everything else (e.g. \N for NULL). Also interprets the
|
42
|
'\n' escape sequence as a newline.'''
|
43
|
def __init__(self, stream, dialect):
|
44
|
assert is_tsv(dialect)
|
45
|
self.stream = stream
|
46
|
self.dialect = dialect
|
47
|
|
48
|
def __iter__(self): return self
|
49
|
|
50
|
def next(self):
|
51
|
record = ''
|
52
|
ending = None
|
53
|
while True:
|
54
|
line = self.stream.readline()
|
55
|
if line == '': raise StopIteration
|
56
|
|
57
|
raw_contents, ending = strings.extract_line_ending(line)
|
58
|
contents = strings.remove_suffix(escape, raw_contents)
|
59
|
record += contents
|
60
|
if len(contents) == len(raw_contents): break # no line continuation
|
61
|
record += ending_placeholder
|
62
|
|
63
|
# Prevent "new-line character seen in unquoted field" errors
|
64
|
record = record.replace('\r', ending_placeholder)
|
65
|
|
66
|
row = csv.reader(StringIO.StringIO(record), self.dialect).next()
|
67
|
return [v.replace(ending_placeholder, '\n') for v in row]
|
68
|
|
69
|
def reader_class(dialect):
|
70
|
if is_tsv(dialect): return TsvReader
|
71
|
else: return csv.reader
|
72
|
|
73
|
def make_reader(stream, dialect): return reader_class(dialect)(stream, dialect)
|
74
|
|
75
|
def reader_and_header(stream):
|
76
|
'''Automatically detects the dialect based on the header line
|
77
|
@return tuple (reader, header)'''
|
78
|
info = stream_info(stream, parse_header=True)
|
79
|
return (make_reader(stream, info.dialect), info.header)
|
80
|
|
81
|
##### csv modifications
|
82
|
|
83
|
# Note that these methods only work on *instances* of Dialect classes
|
84
|
csv.Dialect.__eq__ = lambda self, other: self.__dict__ == other.__dict__
|
85
|
csv.Dialect.__ne__ = lambda self, other: not (self == other)
|
86
|
|
87
|
##### Row filters
|
88
|
|
89
|
class Filter:
|
90
|
'''Wraps a reader, filtering each row'''
|
91
|
def __init__(self, filter_, reader):
|
92
|
self.reader = reader
|
93
|
self.filter = filter_
|
94
|
|
95
|
def __iter__(self): return self
|
96
|
|
97
|
def next(self): return self.filter(self.reader.next())
|
98
|
|
99
|
std_nulls = [r'\N']
|
100
|
empty_nulls = [''] + std_nulls
|
101
|
|
102
|
class NullFilter(Filter):
|
103
|
'''Translates special string values to None'''
|
104
|
def __init__(self, reader, nulls=std_nulls):
|
105
|
map_ = dict.fromkeys(nulls, None)
|
106
|
def filter_(row): return [map_.get(v, v) for v in row]
|
107
|
Filter.__init__(self, filter_, reader)
|
108
|
|
109
|
class StripFilter(Filter):
|
110
|
'''Strips whitespace'''
|
111
|
def __init__(self, reader):
|
112
|
def filter_(row): return [v.strip() for v in row]
|
113
|
Filter.__init__(self, filter_, reader)
|