"""CSVParser.py
A parser for CSV files.
"""
import types
# The states of the parser
StartRecord = 0
StartField = 1
InField = 2
QuoteInField = 3
InQuotedField = 4
QuoteInQuotedField = 5
EndQuotedField = 6
# State handlers can return Finished to terminate parsing early
Finished = 10
class ParseError(Exception):
pass
class CSVParser:
"""Parser for CSV files.
Parses CSV files including all subtleties such as:
* commas in fields
* double quotes in fields
* embedded newlines in fields
- Examples of programs that produce such beasts include
MySQL and Excel
For a higher-level, friendlier CSV class with many conveniences,
see DataTable (which uses this class for its parsing).
Example:
records = []
parse = CSVParser().parse
for line in lines:
results = parse(line)
if results is not None:
records.append(results)
CREDIT
The algorithm was taken directly from the open source Python
C-extension, csv:
http://www.object-craft.com.au/projects/csv/
It would be nice to use the csv module when present, since it is
substantially faster. Before that can be done, it needs to support
allowComments and stripWhitespace, and pass the TestCSVParser.py
test suite.
"""
def __init__(self, allowComments=1, stripWhitespace=1, fieldSep=',',
autoReset=1, doubleQuote=1):
"""Create a new CSV parser.
allowComments: If true (the default), then comment lines using
the Python comment marker are allowed.
stripWhitespace: If true (the default), then left and right whitespace
is stripped off from all fields.
fieldSep: Defines the field separator string (a comma by default).
autoReset: If true (the default), recover from errors automatically.
doubleQuote: If true (the default), assume quotes in fields are
escaped by appearing doubled.
"""
# settings
self._allowComments = allowComments
self._stripWhitespace = stripWhitespace
self._doubleQuote = doubleQuote
self._fieldSep = fieldSep
self._autoReset = autoReset
# Other
self._state = StartRecord
self._fields = []
self._hadParseError = 0
self._field = [] # a list of chars for the cur field
self.addChar = self._field.append
# The handlers for the various states
self._handlers = [
self.startRecord,
self.startField,
self.inField,
self.quoteInField,
self.inQuotedField,
self.quoteInQuotedField,
self.endQuotedField,
]
## Parse ##
def parse(self, line):
"""Parse a single line and return a list of string fields.
Returns None if the CSV record contains embedded newlines and
the record is not yet complete.
"""
if self._autoReset and self._hadParseError:
self.reset()
handlers = self._handlers
i = 0
lineLen = len(line)
while i < lineLen:
c = line[i]
if c == '\r':
i += 1
if i == lineLen:
break # Mac end of line
c = line[i]
if c == '\n':
i += 1
if i == lineLen:
break # Win end of line
self._hadParseError = 1
raise ParseError('Newline inside string')
elif c == '\n':
i += 1
if i == lineLen:
break # unix end of line
self._hadParseError = 1
raise ParseError('Newline inside string')
else:
if handlers[self._state](c) == Finished:
break # process a character
i += 1
handlers[self._state]('\0') # signal the end of the input
if self._state == StartRecord:
fields = self._fields
self._fields = []
if self._stripWhitespace:
fields = [field.strip() for field in fields]
return fields
else:
return None # indicates multi-line record; e.g. not finished
## Reset ##
def reset(self):
"""Reset the parser.
Resets the parser to a fresh state in order to recover from
exceptions. But if autoReset is true (the default), this is
done automatically.
"""
self._fields = []
self._state = StartRecord
self._hadParseError = 0
## State Handlers ##
def startRecord(self, c):
if c != '\0': # not empty line
if c == '#' and self._allowComments:
return Finished
else:
self._state = StartField
self.startField(c)
def startField(self, c):
if c == '"':
self._state = InQuotedField # start quoted field
elif c == self._fieldSep:
self.saveField() # save empty field
elif c == ' ' and self._stripWhitespace:
pass # skip over preceding whitespace
elif c == '\0':
self.saveField() # save empty field
self._state = StartRecord
else:
self.addChar(c) # begin new unquoted field
self._state = InField
def inField(self, c):
# in unquoted field
if c == self._fieldSep:
self.saveField()
self._state = StartField
elif c == '\0':
self.saveField() # end of line
self._state = StartRecord
elif c == '"' and self._doubleQuote:
self._state = QuoteInField
else:
self.addChar(c) # normal character
def quoteInField(self, c):
self.addChar('"')
if c == '"':
self._state = InField # save "" as "
elif c == '\0':
self.saveField() # end of line
self._state = StartRecord
elif c == self._fieldSep:
self.saveField()
self._state = StartField
else:
self.addChar(c) # normal character
self._state = InField
def inQuotedField(self, c):
if c == '"':
if self._doubleQuote:
self._state = QuoteInQuotedField
else:
self.saveField() # end of field
self._state = EndQuotedField
elif c == '\0':
self.addChar('\n') # end of line
else:
self.addChar(c) # normal character
def quoteInQuotedField(self, c):
if c == '"':
self.addChar('"') # save "" as "
self._state = InQuotedField
elif c == self._fieldSep:
self.saveField()
self._state = StartField
elif c == ' ' and self._stripWhitespace:
pass # skip it
elif c == '\0':
self.saveField() # end of line
self._state = StartRecord
else:
self._hadParseError = 1 # illegal
raise ParseError, '%s expected after "' % self._fieldSep
def endQuotedField(self, c):
if c == self._fieldSep: # seen closing " on quoted field
self._state = StartField # wait for new field
elif c == '\0':
self._state = StartRecord # end of line
else:
self._hadParseError = 1
raise ParseError, '%s expected after "' % self._fieldSep
def saveField(self):
self._fields.append(''.join(self._field))
self._field = []
self.addChar = self._field.append
# Call the global function parse() if you like the default settings of the CSVParser
_parser = CSVParser()
parse = _parser.parse
def joinCSVFields(fields):
"""Return a CSV record (e.g. a string) from a sequence of fields.
Fields containing commands (,) or double quotes (") are quoted and
double quotes are escaped (""). The terminating newline is NOT included.
"""
newFields = []
for field in fields:
assert type(field) is types.StringType
if field.find('"') != -1:
newField = '"' + field.replace('"', '""') + '"'
elif field.find(',') != -1:
newField = '"' + field + '"'
else:
newField = field
newFields.append(newField)
return ','.join(newFields)
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