"""
Small scanf implementation.
Python has powerful regular expressions but sometimes they are totally overkill
when you just want to parse a simple-formatted string.
C programmers use the scanf-function for these tasks (see link below).
This implementation of scanf translates the simple scanf-format into
regular expressions. Unlike C you can be sure that there are no buffer overflows
possible.
For more information see
* http://www.python.org/doc/current/lib/node49.html
* http://en.wikipedia.org/wiki/Scanf
Original code from:
http://code.activestate.com/recipes/502213-simple-scanf-implementation/
Modified original to make the %f more robust, as well as added %* modifier to
skip fields.
Version: 1.3.3
Releases:
1.0
2010-10-11
* Initial release
1.1
2010-10-13
* Changed regex from 'match' (only matches at beginning of line)
to 'search' (matches anywhere in line)
* Bugfix - ignore cast for skipped fields
1.2
2013-05-30
* Added 'collapseWhitespace' flag (defaults to True) to take the search
string and replace all whitespace with regex string to match repeated
whitespace. This enables better matching in log files where the data
has been formatted for easier reading. These cases have variable
amounts of whitespace between the columns, depending on the number
of characters in the data itself.
1.3
2016-01-18
* Add 'extractdata' function.
1.3.1
2016-06-23
* Release to PyPi, now including README.md
Updates by Meagan Lang:
2018-04-12
* Added ability to parse components of field specifiers and cope with
whitespace padding.
"""
import re
import sys
from yggdrasil import tools
__version__ = '1.3.3'
__all__ = ["scanf", 'scanf_translate', 'scanf_compile']
DEBUG = False
def no_cast(s):
r"""Dummy function to cast a string to a string.
Args:
s (str): String to cast.
Returns:
str: Cast string.
"""
return s
def cast_str(s):
r"""Cast a string value to a string, stripping whitespace.
Args:
s (str): String to cast.
Returns:
str: Cast string.
"""
return s.strip()
def cast_hex(s):
r"""Cast a string value to a hex integer.
Args:
s (str): String to cast.
Returns:
int: Base 16 integer for provided string.
"""
return int(s, 16)
def cast_oct(s):
r"""Cast a string value to an octal.
Args:
s (str): String to cast.
Returns:
int: Base 8 integer for provided string.
"""
return int(s, 8)
def cformat2regex(flags, width, precision, length, specifier):
r"""Get regex substring that will match the given cformat components.
Args:
flags (str): Format flags.
width (str): Minimum field width.
precision (str): Field precision.
length (str): Field value size (e.g. short, long).
specifier (str): Field specifier.
Returns:
str: Regex expression that will match the provided components.
"""
pat_dec = '[-+]?\\d+(?:\\.\\d+)?'
pat_sub = ''
pad_zero = 0
# Left padding specified in flags
if '0' in flags:
if '+' in flags:
pat_sub += '[-+]'
if width and specifier in 'diueEfgGoxX':
pad_zero = int(width)
else:
if ('-' not in flags) and width and (specifier != 's'):
pat_sub += "\\s{,%s}" % width
if '+' in flags:
pat_sub += '[-+]'
if precision and specifier in 'diuoxX':
pad_zero = max(pad_zero, int(precision[1:]))
# Casts
if pad_zero and specifier in 'diueEfgG':
pat_sub += '0{,%d}' % pad_zero
if specifier == 'f':
pat_sub += pat_dec
elif specifier in 'eE':
pat_sub += '%s%s[+-]\\d+' % (pat_dec, specifier)
elif specifier in 'gG':
pat_sub += '%s(?:[eE][+-]\\d+)?' % (pat_dec)
elif specifier in 'diu':
pat_sub += '\\d+'
elif specifier in 'cs':
if not width:
if specifier == 'c':
pat_sub += '.'
else:
pat_sub += '\\S+'
else:
pat_sub += '.{%s}' % width
elif specifier in 'xX':
if '#' in flags:
pat_sub += '0%s' % specifier
if pad_zero:
pat_sub += '0{,%d}' % pad_zero
pat_sub += '[\\dA-Za-f]+'
elif specifier == 'o':
if '#' in flags:
pat_sub += '0'
if pad_zero:
pat_sub += '0{,%d}' % pad_zero
pat_sub += '[0-7]*'
if ('-' in flags) and ('0' not in flags) and width:
pat_sub += "\\s{,%s}" % width
return pat_sub
def parse_cformat(format, i):
pattern = None
cast = None
# %[flags][width][.precision][length]specifier
# float_format = "%([ -\\+0]{,4})(\\d*)((?:\\.\\d+)?)(L?)([eEfgG])"
# First check for match to complex
complex_format = ("%([ -0]{,3})(\\d*)((?:\\.\\d+)?)([hlL]{,2})([eEfgG])"
+ "%(\\+?[ -0]{,3}\\+?)(\\d*)((?:\\.\\d+)?)([hlL]{,2})([eEfgG])j")
token = re.compile(complex_format)
found = token.match(format, i)
if found:
cast = complex
groups = found.groups()
pat_sub1 = cformat2regex(*groups[:5])
pat_sub2 = cformat2regex(*groups[5:])
pattern = "(%s%sj)" % (pat_sub1, pat_sub2)
return found, pattern, cast
# Then check for generic
any_format = "%([\\* \\-\\+#0]{,6})(\\d*)((?:\\.\\d+)?)([hlL]{,2})([cdieEfgGosuxX])"
token = re.compile(any_format)
found = token.match(format, i)
if found:
groups = found.groupdict() or found.groups()
# Get cast
specifier = groups[-1]
if specifier in 'eEfgG':
cast = float
elif specifier in 'diu':
cast = int
elif specifier == 'c':
cast = no_cast
elif specifier == 's':
cast = cast_str
elif specifier in ['x', 'X']:
cast = cast_hex
elif specifier in ['o']:
cast = cast_oct
else: # pragma: debug
raise Exception('No cast for specifier %s.' % specifier)
# Get pattern
pat_sub = cformat2regex(*groups)
if '*' in groups[0]:
pattern = "(?:%s)" % pat_sub
cast = None
else:
pattern = "(%s)" % pat_sub
return found, pattern, cast
return found, pattern, cast
# As you can probably see it is relatively easy to add more format types.
# Make sure you add a second entry for each new item that adds the extra
# few characters needed to handle the field ommision.
scanf_translate = [
(re.compile(_token), _pattern, _cast) for _token, _pattern, _cast in [
("%c", "(.)", lambda x:x),
("%\\*c", "(?:.)", None),
("%(\\d)c", "(.{%s})", lambda x:x),
("%\\*(\\d)c", "(?:.{%s})", None),
("%(\\d)[di]", "([+-]?\\d{%s})", int),
("%\\*(\\d)[di]", "(?:[+-]?\\d{%s})", None),
("%-(\\d)[di]", "(.{%s})", int),
("%\\*-(\\d)[di]", "(?:.{%s})", None),
("%[di]", "([+-]?\\d+)", int),
("%\\*[di]", "(?:[+-]?\\d+)", None),
("%u", "(\\d+)", int),
("%\\*u", "(?:\\d+)", None),
# langmm: complex
("%[fgeE]%[+-][fgeE]j",
"("
+ "(?:[-+]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][-+]?\\d+)?)"
+ "[+-]"
+ "(?:(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][-+]?\\d+)?)"
+ "j)",
complex),
("%\\*[fgeE]%[+-][fgeE]j",
"(?:"
+ "(?:[-+]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][-+]?\\d+)?)"
+ "[+-]"
+ "(?:(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][-+]?\\d+)?)"
+ "j)",
None),
("%[fgeE]", "([-+]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][-+]?\\d+)?)", float),
("%\\*[fgeE]", "(?:[-+]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][-+]?\\d+)?)", None),
# langmm: Added to allows matching of %5s
("%(\\d)s", "(.{%s})", lambda x:x.strip()),
("%\\*(\\d)s", "(?:.{%s})", None),
("%s", "(\\S+)", lambda x:x),
("%\\*s", "(?:\\S+)", None),
("%([xX])", "(0%s[\\dA-Za-f]+)", lambda x:int(x, 16)),
("%\\*([xX])", "(?:0%s[\\dA-Za-f]+)", None),
("%o", "(0[0-7]*)", lambda x:int(x, 8)),
("%\\*o", "(?:0[0-7]*)", None),
]]
# Cache formats
SCANF_CACHE_SIZE = 1000
scanf_cache = {}
[docs]def scanf_compile(format, collapseWhitespace=True):
"""
Translate the format into a regular expression
For example:
>>> format_re, casts = _scanf_compile('%s - %d errors, %d warnings')
>>> print format_re.pattern
(\\S+) \\- ([+-]?\\d+) errors, ([+-]?\\d+) warnings
Translated formats are cached for faster reuse
"""
compiled = scanf_cache.get(format)
if compiled:
return compiled
format_pat = ""
cast_list = []
i = 0
length = len(format)
while i < length:
found = None
found, pattern, cast = parse_cformat(format, i)
if found:
if cast:
cast_list.append(cast)
format_pat += pattern
i = found.end()
# for token, pattern, cast in scanf_translate:
# found = token.match(format, i)
# if found:
# print('found', pattern)
# if cast: # cast != None
# cast_list.append(cast)
# groups = found.groupdict() or found.groups()
# if groups:
# pattern = pattern % groups
# format_pat += pattern
# i = found.end()
# break
if not found:
char = format[i]
# escape special characters
if char in "()[]-.+*?{}<>\\":
format_pat += "\\"
format_pat += char
i += 1
if DEBUG:
print("DEBUG: %r -> %s" % (format, format_pat))
if collapseWhitespace:
format_pat = re.sub('\\s+', r'\\s+', format_pat)
format_re = re.compile(format_pat)
if len(scanf_cache) > SCANF_CACHE_SIZE:
scanf_cache.clear()
scanf_cache[format] = (format_re, cast_list)
return format_re, cast_list
[docs]def scanf(format, s=None, collapseWhitespace=True):
"""
scanf supports the following formats:
%c One character
%5c 5 characters
%d, %i int value
%7d, %7i int value with length 7
%f float value
%o octal value
%X, %x hex value
%s string terminated by whitespace
Examples:
>>> scanf("%s - %d errors, %d warnings", "/usr/sbin/sendmail - 0 errors, 4 warnings")
('/usr/sbin/sendmail', 0, 4)
>>> scanf("%o %x %d", "0123 0x123 123")
(66, 291, 123)
If the parameter s is a file-like object, s.readline is called.
If s is not specified, stdin is assumed.
The function returns a tuple of found values
or None if the format does not match.
"""
if s is None:
s = sys.stdin
if hasattr(s, "readline"):
s = s.readline()
as_bytes = False
if isinstance(s, bytes):
as_bytes = True
s = s.decode("utf-8")
format = tools.bytes2str(format)
# print(s, format)
format_re, casts = scanf_compile(format, collapseWhitespace)
found = format_re.search(s)
if found:
groups = found.groups()
out = [casts[i](groups[i]) for i in range(len(groups))]
if as_bytes:
for i in range(len(out)):
if isinstance(out[i], str):
out[i] = out[i].encode("utf-8")
return tuple(out)
def extractdata(pattern, text=None, filepath=None):
"""
Read through an entire file or body of text one line at a time. Parse each
line that matches the supplied pattern string and ignore the rest.
If *text* is supplied, it will be parsed according to the *pattern* string.
If *text* is not supplied, the file at *filepath* will be opened and parsed.
"""
y = []
if text is None:
with open(filepath) as f:
for line in f:
match = scanf(pattern, line)
if match:
if len(y) == 0:
y = [[float(s)] for s in match]
else:
for i, ydata in enumerate(y):
ydata.append(float(match[i]))
else:
for line in text.split('\n'):
match = scanf(pattern, line)
if match:
if len(y) == 0:
y = [[float(s)] for s in match]
else:
for i, ydata in enumerate(y):
ydata.append(float(match[i]))
return y
if __name__ == "__main__":
import doctest
doctest.testmod(verbose=True, report=True)