cs.lex 20210906

Lexical analysis functions, tokenisers, transcribers: an arbitrary assortment of lexical and tokenisation functions useful for writing recursive descent parsers, of which I have several. There are also some transcription functions for producing text from various objects, such as `hexify` and `unctrl`.

Lexical analysis functions, tokenisers, transcribers: an arbitrary assortment of lexical and tokenisation functions useful for writing recursive descent parsers, of which I have several. There are also some transcription functions for producing text from various objects, such as hexify and unctrl.

Latest release 20210906: New strip_prefix_n() function to strip a leading prefix and numeric value n from the start of a string.

Generally the get_* functions accept a source string and an offset (usually optional, default 0) and return a token and the new offset, raising ValueError on failed tokenisation.

Function as_lines(chunks, partials=None)

Generator yielding complete lines from arbitrary pieces of text from the iterable of str chunks.

After completion, any remaining newline-free chunks remain in the partials list; they will be unavailable to the caller unless the list is presupplied.

Function common_prefix(*strs)

Return the common prefix of the strings strs.

Examples:

>>> common_prefix('abc', 'def')
''
>>> common_prefix('abc', 'abd')
'ab'
>>> common_prefix('abc', 'abcdef')
'abc'
>>> common_prefix('abc', 'abcdef', 'abz')
'ab'
>>> # contrast with cs.fileutils.common_path_prefix
>>> common_prefix('abc/def', 'abc/def1', 'abc/def2')
'abc/def'

Function common_suffix(*strs)

Return the common suffix of the strings strs.

Function cropped(s: str, max_length: int = 32, roffset: int = 1, ellipsis: str = '...')

If the length of s exceeds max_length (default 32), replace enough of the tail with ellipsis and the last roffset (default 1) characters of s to fit in max_length characters.

Function cropped_repr(o, roffset=1, max_length=32, inner_max_length=None)

Compute a cropped repr() of o.

Parameters:

• o: the object to represent
• max_length: the maximum length of the representation, default 32
• inner_max_length: the maximum length of the representations of members of o, default max_length//2
• roffset: the number of trailing characters to preserve, default 1

Function cutprefix(s, prefix)

Strip a prefix from the front of s. Return the suffix if s.startswith(prefix), else s.

Example:

>>> abc_def = 'abc.def'
>>> cutprefix(abc_def, 'abc.')
'def'
>>> cutprefix(abc_def, 'zzz.')
'abc.def'
>>> cutprefix(abc_def, '.zzz') is abc_def
True

Function cutsuffix(s, suffix)

Strip a suffix from the end of s. Return the prefix if s.endswith(suffix), else s.

Example:

>>> abc_def = 'abc.def'
>>> cutsuffix(abc_def, '.def')
'abc'
>>> cutsuffix(abc_def, '.zzz')
'abc.def'
>>> cutsuffix(abc_def, '.zzz') is abc_def
True

Function format_as(format_s: str, format_mapping, formatter=None, error_sep=None)

Format the string format_s using Formatter.vformat, return the formatted result. This is a wrapper for str.format_map which raises a more informative FormatAsError exception on failure.

Parameters:

• format_s: the format string to use as the template
• format_mapping: the mapping of available replacement fields
• formatter: an optional string.Formatter-like instance with a .vformat(format_string,args,kwargs) method, usually a subclass of string.Formatter; if not specified then str.Formatter is used
• error_sep: optional separator for the multipart error message, default from FormatAsError.DEFAULT_SEPARATOR: '; '

Function format_attribute(method)

Mark a method as available as a format method. Requires the enclosing class to be decorated with @has_format_attributes.

Function format_escape(s)

Escape {} characters in a string to protect them from str.format.

Function format_recover(*da, **dkw)

Decorator for __format__ methods which replaces failed formats with {self:format_spec}.

Class FormatableFormatter(string.Formatter)

A string.Formatter subclass interacting with objects which inherit from FormatableMixin.

Method FormatableFormatter.format_field(*a, **kw)

Format a value using value.format_format_field, returning an FStr (a str subclass with additional format_spec features).

We actually recognise colon separated chains of formats and apply each format to the previously converted value. str values are promoted to FStr at each step.

At each step, for the current value we try format(value) first then FormattableMixin.convert_via_method_or_attr(value) then FormattableMixin.convert_via_method_or_attr(FStr(value)) in turn.

Method FormatableFormatter.format_field1(value, format_subspec)

Format a subspec of a larger colon separated format_spec as from format_field(value,format_spec). Return the new value, which need not be a str; the outer format_field call does a final conversion to an FStr.

Method FormatableFormatter.get_arg_name(field_name)

Default initial arg_name is an identifier.

Returns (prefix,offset), and ('',0) if there is no arg_name.

Method FormatableFormatter.get_field(self, *a, **kw)

Get the object referenced by the field text field_name.

Method FormatableFormatter.get_format_subspecs(format_spec)

Parse a format_spec as a sequence of colon separated components, return the components.

Method FormatableFormatter.get_subfield(value, subfield_text: str)

Resolve value against subfield_text, the remaining field text after the term which resolved to value.

For example, a format {name.blah[0]} has the field text name.blah[0]. A get_field implementation might initially resolve name to some value, leaving .blah[0] as the subfield_text. This method supports taking that value and resolving it against the remaining text .blah[0].

For generality, if subfield_text is the empty string value is returned unchanged.

Method FormatableFormatter.get_value(self, *a, **kw)

Get the object with index arg_name.

This default implementation returns (kw[arg_name],arg_name).

Class FormatableMixin(FormatableFormatter,string.Formatter)

A subclass of FormatableFormatter which provides 2 features:

• a __format__ method which parses the format_spec` string into multiple colon separated terms whose results chain
• a format_as method which formats a format string using str.format_map with a suitable mapping derived from the instance via its format_kwargs method (whose default is to return the instance itself)

The format_as method is like an inside out str.format or object.__format__ method.

The str.format method is designed for formatting a string from a variety of other objects supplied in the keyword arguments.

The object.__format__ method is for filling out a single str.format replacement field from a single object.

By contrast, format_as is designed to fill out an entire format string from the current object.

For example, the cs.tagset.TagSetMixin class uses FormatableMixin to provide a format_as method whose replacement fields are derived from the tags in the tag set.

Subclasses wanting to provide additional format_spec terms should:

• override FormatableFormatter.format_field1 to implement terms with no colons, letting format_field do the split into terms
• override FormatableFormatter.get_format_subspecs to implement the parse of format_spec into a sequence of terms. This might recognise a special additional syntax and quietly fall back to super().get_format_subspecs if that is not present.

Method FormatableMixin.__format__(self, format_spec)

Format self according to format_spec.

This implementation calls self.format_field. As such, a format_spec is considered a sequence of colon separated terms.

Classes wanting to implement addition format string syntaxes should either:

• override FormatableFormatter.format_field1 to implement terms with no colons, letting format_field1 do the split into terms
• override FormatableFormatter.get_format_subspecs to implement the term parse.

The default implementation of __format1__ just calls super().__format__. Implementations providing specialised formats should implement them in __format1__ with fallback to super().__format1__.

Method FormatableMixin.convert_field(self, value, conversion)

Default converter for fields calls Formatter.convert_field.

Method FormatableMixin.convert_via_method_or_attr(self, *a, **kw)

Apply a method or attribute name based conversion to value where format_spec starts with a method name applicable to value. Return (converted,offset) being the converted value and the offset after the method name.

The methods/attributes are looked up in the mapping returned by .format_attributes() which represents allowed methods (broadly, one should not allow methods which modify any state).

If this returns a callable, it is called to obtain the converted value otherwise it is used as is.

As a final tweak, if value.get_format_attribute() raises an AttributeError (the attribute is not an allowed attribute) or calling the attribute raises a TypeError (the value isn't suitable) and the value is not an instance of FStr, convert it to an FStr and try again. This provides the command utility methods on other types.

The motivating example was a PurePosixPath, which does not JSON transcribe; this tweak supports both posixpath:basename via the pathlib stuff and posixpath:json via FStr even though a PurePosixPath does not subclass FStr.

Method FormatableMixin.format_as(self, format_s, error_sep=None, **control_kw)

Return the string format_s formatted using the mapping returned by self.format_kwargs(**control_kw).

If a class using the mixin has no format_kwargs(**control_kw) method to provide a mapping for str.format_map then the instance itself is used as the mapping.

Method FormatableMixin.get_format_attribute(self, attr)

Return a mapping of permitted methods to functions of an instance. This is used to whitelist allowed :name method formats to prevent scenarios like little Bobby Tables calling delete().

Method FormatableMixin.get_format_attributes()

Return the mapping of format attributes.

Method FormatableMixin.json(self)

The value transcribed as compact JSON.

Class FormatAsError(builtins.LookupError,builtins.Exception,builtins.BaseException)

Subclass of LookupError for use by format_as.

Class FStr(FormatableMixin,FormatableFormatter,string.Formatter,builtins.str)

A str subclass with the FormatableMixin methods, particularly its __format__ which use str method names as valid formats.

It also has a bunch of utility methods which are available as :method in format strings.

Method FStr.basename(self)

Treat as a filesystem path and return the basename.

Method FStr.dirname(self)

Treat as a filesystem path and return the dirname.

Method FStr.f(self)

Parse self as a float.

Method FStr.i(self, base=10)

Parse self as an int.

Method FStr.lc(self)

Lowercase using lc_().

Method FStr.path(self)

Convert to a native filesystem pathlib.Path.

Method FStr.posix_path(self)

Convert to a Posix filesystem pathlib.Path.

Method FStr.windows_path(self)

Convert to a Windows filesystem pathlib.Path.

Function get_chars(s, offset, gochars)

Scan the string s for characters in gochars starting at offset. Return (match,new_offset).

gochars may also be a callable, in which case a character ch is accepted if gochars(ch) is true.

Function get_decimal(s, offset=0)

Scan the string s for decimal characters starting at offset (default 0). Return (dec_string,new_offset).

Function get_decimal_or_float_value(s, offset=0)

Fetch a decimal or basic float (nnn.nnn) value from the str s at offset (default 0). Return (value,new_offset).

Function get_decimal_value(s, offset=0)

Scan the string s for a decimal value starting at offset (default 0). Return (value,new_offset).

Function get_delimited(s, offset, delim)

Collect text from the string s from position offset up to the first occurence of delimiter delim; return the text excluding the delimiter and the offset after the delimiter.

Function get_dotted_identifier(s, offset=0, **kw)

Scan the string s for a dotted identifier (by default an ASCII letter or underscore followed by letters, digits or underscores) with optional trailing dot and another dotted identifier, starting at offset (default 0). Return (match,new_offset).

Note: the empty string and an unchanged offset will be returned if there is no leading letter/underscore.

Keyword arguments are passed to get_identifier (used for each component of the dotted identifier).

Function get_envvar(s, offset=0, environ=None, default=None, specials=None)

Parse a simple environment variable reference to $varname or $x where "x" is a special character.

Parameters:

• s: the string with the variable reference
• offset: the starting point for the reference
• default: default value for missing environment variables; if None (the default) a ValueError is raised
• environ: the environment mapping, default os.environ
• specials: the mapping of special single character variables

Function get_hexadecimal(s, offset=0)

Scan the string s for hexadecimal characters starting at offset (default 0). Return (hex_string,new_offset).

Function get_hexadecimal_value(s, offset=0)

Scan the string s for a hexadecimal value starting at offset (default 0). Return (value,new_offset).

Function get_identifier(s, offset=0, alpha='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', number='0123456789', extras='_')

Scan the string s for an identifier (by default an ASCII letter or underscore followed by letters, digits or underscores) starting at offset (default 0). Return (match,new_offset).

Note: the empty string and an unchanged offset will be returned if there is no leading letter/underscore.

Parameters:

• s: the string to scan
• offset: the starting offset, default 0.
• alpha: the characters considered alphabetic, default string.ascii_letters.
• number: the characters considered numeric, default string.digits.
• extras: extra characters considered part of an identifier, default '_'.

Function get_ini_clause_entryname(s, offset=0)

Parse a [clausename]entryname string from s at offset (default 0). Return (clausename,entryname,new_offset).

Function get_ini_clausename(s, offset=0)

Parse a [clausename] string from s at offset (default 0). Return (clausename,new_offset).

Function get_nonwhite(s, offset=0)

Scan the string s for characters not in string.whitespace starting at offset (default 0). Return (match,new_offset).

Function get_other_chars(s, offset=0, stopchars=None)

Scan the string s for characters not in stopchars starting at offset (default 0). Return (match,new_offset).

Function get_qstr(s, offset=0, q='"', environ=None, default=None, env_specials=None)

Get quoted text with slosh escapes and optional environment substitution.

Parameters:

• s: the string containg the quoted text.
• offset: the starting point, default 0.
• q: the quote character, default '"'. If q is None, do not expect the string to be delimited by quote marks.
• environ: if not None, also parse and expand $envvar references.
• default: passed to get_envvar

Function get_qstr_or_identifier(s, offset)

Parse a double quoted string or an identifier.

Function get_sloshed_text(s, delim, offset=0, slosh='\\', mapper=<function slosh_mapper at 0x1049cd8b0>, specials=None)

Collect slosh escaped text from the string s from position offset (default 0) and return the decoded unicode string and the offset of the completed parse.

Parameters:

• delim: end of string delimiter, such as a single or double quote.
• offset: starting offset within s, default 0.
• slosh: escape character, default a slosh ('').
• mapper: a mapping function which accepts a single character and returns a replacement string or None; this is used the replace things such as '\t' or '\n'. The default is the slosh_mapper function, whose default mapping is SLOSH_CHARMAP.
• specials: a mapping of other special character sequences and parse functions for gathering them up. When one of the special character sequences is found in the string, the parse function is called to parse at that point. The parse functions accept s and the offset of the special character. They return the decoded string and the offset past the parse.

The escape character slosh introduces an encoding of some replacement text whose value depends on the following character. If the following character is:

• the escape character slosh, insert the escape character.
• the string delimiter delim, insert the delimiter.
• the character 'x', insert the character with code from the following 2 hexadecimal digits.
• the character 'u', insert the character with code from the following 4 hexadecimal digits.
• the character 'U', insert the character with code from the following 8 hexadecimal digits.
• a character from the keys of mapper

Function get_tokens(s, offset, getters)

Parse the string s from position offset using the supplied tokeniser functions getters. Return the list of tokens matched and the final offset.

Parameters:

• s: the string to parse.
• offset: the starting position for the parse.
• getters: an iterable of tokeniser specifications.

Each tokeniser specification getter is either:

• a callable expecting (s,offset) and returning (token,new_offset)
• a literal string, to be matched exactly
• a tuple or list with values (func,args,kwargs); call func(s,offset,*args,**kwargs)
• an object with a .match method such as a regex; call getter.match(s,offset) and return a match object with a .end() method returning the offset of the end of the match

Function get_uc_identifier(s, offset=0, number='0123456789', extras='_')

Scan the string s for an identifier as for get_identifier, but require the letters to be uppercase.

Function get_white(s, offset=0)

Scan the string s for characters in string.whitespace starting at offset (default 0). Return (match,new_offset).

Function has_format_attributes(cls)

Class decorator to walk this class for direct methods marked as for use in format strings and to include them in cls.format_attributes().

Function hexify(bs)

A flavour of binascii.hexlify returning a str.

Function htmlify(s, nbsp=False)

Convert a string for safe transcription in HTML.

Parameters:

• s: the string
• nbsp: replaces spaces with " " to prevent word folding, default False.

Function htmlquote(s)

Quote a string for use in HTML.

Function is_dotted_identifier(s, offset=0, **kw)

Test if the string s is an identifier from position offset onward.

Function is_identifier(s, offset=0, **kw)

Test if the string s is an identifier from position offset (default 0) onward.

Function isUC_(s)

Check that a string matches the regular expression ^[A-Z][A-Z_0-9]*$.

Function jsquote(s)

Quote a string for use in JavaScript.

Function lc_(value)

Return value.lower() with '-' translated into '_' and ' ' translated into '-'.

I use this to construct lowercase filenames containing a readable transcription of a title string.

See also titleify_lc(), an imperfect reversal of this.

Function match_tokens(s, offset, getters)

Wrapper for get_tokens which catches ValueError exceptions and returns (None,offset).

Function parseUC_sAttr(attr)

Take an attribute name attr and return (key,is_plural).

Examples:

• 'FOO' returns ('FOO',False).
• 'FOOs' or 'FOOes' returns ('FOO',True). Otherwise return (None,False).

Function phpquote(s)

Quote a string for use in PHP code.

Function skipwhite(s, offset=0)

Convenience routine for skipping past whitespace; returns the offset of the next nonwhitespace character.

Function slosh_mapper(c, charmap=None)

Return a string to replace backslash-c, or None.

Function strip_prefix_n(s, prefix, n=None)

Strip a leading prefix and numeric value n from the start of a string. Return the remaining string, or the original string if the prefix or numeric value do not match.

Parameters:

• s: the string to strip
• prefix: the prefix string which must appear at the start of s
• n: optional integer value; if omitted any value will be accepted, otherise the numeric part must match n

Examples:

strip_prefix_n('s03e01--', 's', 3) 'e01--' strip_prefix_n('s03e01--', 's', 4) 's03e01--' strip_prefix_n('s03e01--', 's') 'e01--'

Function stripped_dedent(s)

Slightly smarter dedent which ignores a string's opening indent.

Algorithm: strip the supplied string s, pull off the leading line, dedent the rest, put back the leading line.

This supports my preferred docstring layout, where the opening line of text is on the same line as the opening quote.

Example:

>>> def func(s):
...   """ Slightly smarter dedent which ignores a string's opening indent.
...       Strip the supplied string `s`. Pull off the leading line.
...       Dedent the rest. Put back the leading line.
...   """
...   pass
...
>>> from cs.lex import stripped_dedent
>>> print(stripped_dedent(func.__doc__))
Slightly smarter dedent which ignores a string's opening indent.
Strip the supplied string `s`. Pull off the leading line.
Dedent the rest. Put back the leading line.

Function strlist(ary, sep=', ')

Convert an iterable to strings and join with sep (default ', ').

Function tabpadding(padlen, tabsize=8, offset=0)

Compute some spaces to use a tab padding at an offfset.

Function texthexify(bs, shiftin='[', shiftout=']', whitelist=None)

Transcribe the bytes bs to text using compact text runs for some common text values.

This can be reversed with the untexthexify function.

This is an ad doc format devised to be compact but also to expose "text" embedded within to the eye. The original use case was transcribing a binary directory entry format, where the filename parts would be somewhat visible in the transcription.

The output is a string of hexadecimal digits for the encoded bytes except for runs of values from the whitelist, which are enclosed in the shiftin and shiftout markers and transcribed as is. The default whitelist is values of the ASCII letters, the decimal digits and the punctuation characters '_-+.,'. The default shiftin and shiftout markers are '[' and ']'.

String objects converted with either hexify and texthexify output strings may be freely concatenated and decoded with untexthexify.

Example:

>>> texthexify(b'&^%&^%abcdefghi)(*)(*')
'265e25265e25[abcdefghi]29282a29282a'

Parameters:

• bs: the bytes to transcribe
• shiftin: Optional. The marker string used to indicate a shift to direct textual transcription of the bytes, default: '['.
• shiftout: Optional. The marker string used to indicate a shift from text mode back into hexadecimal transcription, default ']'.
• whitelist: an optional bytes or string object indicating byte values which may be represented directly in text; the default value is the ASCII letters, the decimal digits and the punctuation characters '_-+.,'.

Function titleify_lc(value_lc)

Translate '-' into ' ' and '_' translated into '-', then titlecased.

See also lc_(), which this reverses imperfectly.

Function typed_repr(o, use_cls=False, max_length=None)

Like typed_str but using repr instead of str.

Function typed_str(o, use_cls=False, use_repr=False, max_length=None)

Return "type(o).name:str(o)" for some object o.

Parameters:

• use_cls: default False; if true, use str(type(o)) instead of type(o).__name__
• use_repr: default False; if true, use repr(o) instead of str(o)

I use this a lot when debugging. Example:

from cs.lex import typed_str as s
......
X("foo = %s", s(foo))

Function unctrl(s, tabsize=8)

Return the string s with TABs expanded and control characters replaced with printable representations.

Function untexthexify(s, shiftin='[', shiftout=']')

Decode a textual representation of binary data into binary data.

This is the reverse of the texthexify function.

Outside of the shiftin/shiftout markers the binary data are represented as hexadecimal. Within the markers the bytes have the values of the ordinals of the characters.

Example:

>>> untexthexify('265e25265e25[abcdefghi]29282a29282a')
b'&^%&^%abcdefghi)(*)(*'

Parameters:

• s: the string containing the text representation.
• shiftin: Optional. The marker string commencing a sequence of direct text transcription, default '['.
• shiftout: Optional. The marker string ending a sequence of direct text transcription, default ']'.

Release Log

Release 20210906: New strip_prefix_n() function to strip a leading prefix and numeric value n from the start of a string.

Release 20210717:

• Many many changes to FormatableMixin, FormatableFormatter and friends around supporting {foo|conv1|con2|...} instead of {foo!conv}. Still in flux.
• New typed_repr like typed_str but using repr.

Release 20210306:

• New cropped() function to crop strings.
• Rework cropped_repr() to do the repr() itself, and to crop the interiors of tuples and lists.
• cropped_repr: new inner_max_length for cropping the members of collections.
• cropped_repr: special case for length=1 tuples.
• New typed_str(o) object returning type(o).name:str(o) in the default case, useful for debugging.

Release 20201228: Minor doc updates.

Release 20200914:

• Hide terribly special purpose lastlinelen() in cs.hier under a private name.
• New common_prefix and common_suffix function to compare strings.

Release 20200718: get_chars: accept a callable for gochars, indicating a per character test function.

Release 20200613: cropped_repr: replace hardwired 29 with computed length

Release 20200517:

• New get_ini_clausename to parse "[clausename]".
• New get_ini_clause_entryname parsing "[clausename]entryname".
• New cropped_repr for returning a shortened repr()+"..." if the length exceeds a threshold.
• New format_escape function to double {} characters to survive str.format.

Release 20200318:

• New lc_() function to lowercase and dash a string, new titleify_lc() to mostly reverse lc_().
• New format_as function, FormatableMixin and related FormatAsError.

Release 20200229: New cutprefix and cutsuffix functions.

Release 20190812: Fix bad slosh escapes in strings.

Release 20190220: New function get_qstr_or_identifier.

Release 20181108: new function get_decimal_or_float_value to read a decimal or basic float

Release 20180815: No semantic changes; update some docstrings and clean some lint, fix a unit test.

Release 20180810:

• New get_decimal_value and get_hexadecimal_value functions.
• New stripped_dedent function, a slightly smarter textwrap.dedent.

Release 20171231: New function get_decimal. Drop unused function dict2js.

Release 20170904: Python 2/3 ports, move rfc2047 into new cs.rfc2047 module.

Release 20160828:

• Use "install_requires" instead of "requires" in DISTINFO.
• Discard str1(), pointless optimisation.
• unrfc2047: map _ to SPACE, improve exception handling.
• Add phpquote: quote a string for use in PHP code; add docstring to jsquote.
• Add is_identifier test.
• Add get_dotted_identifier.
• Add is_dotted_identifier.
• Add get_hexadecimal.
• Add skipwhite, convenince wrapper for get_white returning just the next offset.
• Assorted bugfixes and improvements.

Release 20150120: cs.lex: texthexify: backport to python 2 using cs.py3 bytes type

Release 20150118: metadata updates

Release 20150116: PyPI metadata and slight code cleanup.