"""ezt.py -- easy templating
ezt templates are very similar to standard HTML files. But additionally
they contain directives sprinkled in between. With these directives
it is possible to generate the dynamic content from the ezt templates.
These directives are enclosed in square brackets. If you are a
C-programmer, you might be familar with the #ifdef directives of the
C preprocessor 'cpp'. ezt provides a similar concept for HTML. Additionally
EZT has a 'for' directive, which allows to iterate (repeat) certain
subsections of the template according to sequence of data items
provided by the application.
The HTML rendering is performed by the method generate() of the Template
class. Building template instances can either be done using external
EZT files (convention: use the suffix .ezt for such files):
>>> template = Template("../templates/log.ezt")
or by calling the parse() method of a template instance directly with
a EZT template string:
>>> template = Template()
>>> template.parse('''<html><head>
... <title>[title_string]</title></head>
... <body><h1>[title_string]</h1>
... [for a_sequence] <p>[a_sequence]</p>
... [end] <hr>
... The [person] is [if-any state]in[else]out[end].
... </body>
... </html>
... ''')
The application should build a dictionary 'data' and pass it together
with the output fileobject to the templates generate method:
>>> data = {'title_string' : "A Dummy Page",
... 'a_sequence' : ['list item 1', 'list item 2', 'another element'],
... 'person': "doctor",
... 'state' : None }
>>> import sys
>>> template.generate(sys.stdout, data)
<html><head>
<title>A Dummy Page</title></head>
<body><h1>A Dummy Page</h1>
<p>list item 1</p>
<p>list item 2</p>
<p>another element</p>
<hr>
The doctor is out.
</body>
</html>
Template syntax error reporting should be improved. Currently it is
very sparse (template line numbers would be nice):
>>> Template().parse("[if-any where] foo [else] bar [end unexpected args]")
Traceback (innermost last):
File "<stdin>", line 1, in ?
File "ezt.py", line 220, in parse
self.program = self._parse(text)
File "ezt.py", line 275, in _parse
raise ArgCountSyntaxError(str(args[1:]))
ArgCountSyntaxError: ['unexpected', 'args']
>>> Template().parse("[if unmatched_end]foo[end]")
Traceback (innermost last):
File "<stdin>", line 1, in ?
File "ezt.py", line 206, in parse
self.program = self._parse(text)
File "ezt.py", line 266, in _parse
raise UnmatchedEndError()
UnmatchedEndError
Directives
==========
Several directives allow the use of dotted qualified names refering to objects
or attributes of objects contained in the data dictionary given to the
.generate() method.
Simple directives
-----------------
[QUAL_NAME]
This directive is simply replaced by the value of identifier from the data
dictionary. QUAL_NAME might be a dotted qualified name refering to some
instance attribute of objects contained in the dats dictionary.
Numbers are converted to string though.
[include "filename"] or [include QUAL_NAME]
This directive is replaced by content of the named include file.
Block directives
----------------
[for QUAL_NAME] ... [end]
The text within the [for ...] directive and the corresponding [end]
is repeated for each element in the sequence referred to by the qualified
name in the for directive. Within the for block this identifiers now
refers to the actual item indexed by this loop iteration.
[if-any QUAL_NAME [QUAL_NAME2 ...]] ... [else] ... [end]
Test if any QUAL_NAME value is not None or an empty string or list.
The [else] clause is optional. CAUTION: Numeric values are converted to
string, so if QUAL_NAME refers to a numeric value 0, the then-clause is
substituted!
[if-index INDEX_FROM_FOR odd] ... [else] ... [end]
[if-index INDEX_FROM_FOR even] ... [else] ... [end]
[if-index INDEX_FROM_FOR first] ... [else] ... [end]
[if-index INDEX_FROM_FOR last] ... [else] ... [end]
[if-index INDEX_FROM_FOR NUMBER] ... [else] ... [end]
These five directives work similar to [if-any], but are only useful
within a [for ...]-block (see above). The odd/even directives are
for example useful to choose different background colors for adjacent rows
in a table. Similar the first/last directives might be used to
remove certain parts (for example "Diff to previous" doesn't make sense,
if there is no previous).
[is QUAL_NAME STRING] ... [else] ... [end]
[is QUAL_NAME QUAL_NAME] ... [else] ... [end]
The [is ...] directive is similar to the other conditional directives
above. But it allows to compare two value references or a value reference
with some constant string.
"""
import string
import re
from types import StringType, IntType, FloatType
import os
_item = r'(?:"(?:[^\\"]|\\.)*"|[-\w.]+)'
_re_parse = re.compile(r'\[(%s(?: +%s)*)\]|(\[\[\])|\[#[^\]]*\]' % (_item, _item))
_re_args = re.compile(r'"(?:[^\\"]|\\.)*"|[-\w.]+')
_block_cmd_specs = { 'if-index':2, 'for':1, 'is':2 }
_block_cmds = list(_block_cmd_specs.keys())
_re_newline = re.compile('[ \t\r\f\v]*\n\\s*')
_re_whitespace = re.compile(r'\s\s+')
_re_subst = re.compile('%(%|[0-9]+)')
class Template:
def __init__(self, fname=None, compress_whitespace=1):
self.compress_whitespace = compress_whitespace
if fname:
self.parse_file(fname)
def parse_file(self, fname):
"fname -> a string object with pathname of file containg an EZT template."
self.program = self._parse(_FileReader(fname))
def parse(self, text_or_reader):
"""Parse the template specified by text_or_reader.
The argument should be a string containing the template, or it should
specify a subclass of ezt.Reader which can read templates.
"""
if not isinstance(text_or_reader, Reader):
text_or_reader = _TextReader(text_or_reader)
self.program = self._parse(text_or_reader)
def generate(self, fp, data):
ctx = _context()
ctx.data = data
ctx.for_index = { }
self._execute(self.program, fp, ctx)
def _parse(self, reader, for_names=None, file_args=()):
"""text -> string object containing the HTML template.
This is a private helper function doing the real work for method parse.
It returns the parsed template as a 'program'. This program is a sequence
made out of strings or (function, argument) 2-tuples.
Note: comment directives [# ...] are automatically dropped by _re_parse.
"""
parts = _re_parse.split(reader.text)
program = [ ]
stack = [ ]
if not for_names:
for_names = [ ]
for i in range(len(parts)):
piece = parts[i]
which = i % 3 if which == 0:
if piece:
if self.compress_whitespace:
piece = _re_whitespace.sub(' ', _re_newline.sub('\n', piece))
program.append(piece)
elif which == 2:
if piece:
program.append('[')
elif piece:
args = _re_args.findall(piece)
cmd = args[0]
if cmd == 'else':
if len(args) > 1:
raise ArgCountSyntaxError(str(args[1:]))
idx = stack[-1][1]
true_section = program[idx:]
del program[idx:]
stack[-1][3] = true_section
elif cmd == 'end':
if len(args) > 1:
raise ArgCountSyntaxError(str(args[1:]))
try:
cmd, idx, args, true_section = stack.pop()
except IndexError:
raise UnmatchedEndError()
else_section = program[idx:]
func = getattr(self, '_cmd_' + re.sub('-', '_', cmd))
program[idx:] = [ (func, (args, true_section, else_section)) ]
if cmd == 'for':
for_names.pop()
elif cmd in _block_cmds:
if len(args) > _block_cmd_specs[cmd] + 1:
raise ArgCountSyntaxError(str(args[1:]))
args[1] = _prepare_ref(args[1], for_names, file_args)
if cmd == 'is':
args[2] = _prepare_ref(args[2], for_names, file_args)
elif cmd == 'for':
for_names.append(args[1][0])
stack.append([cmd, len(program), args[1:], None])
elif cmd == 'include':
if args[1][0] == '"':
include_filename = args[1][1:-1]
f_args = [ ]
for arg in args[2:]:
f_args.append(_prepare_ref(arg, for_names, file_args))
program.extend(self._parse(reader.read_other(include_filename),
for_names,
f_args))
else:
if len(args) != 2:
raise ArgCountSyntaxError(str(args))
program.append((self._cmd_include,
(_prepare_ref(args[1], for_names, file_args),
reader)))
elif cmd == 'if-any':
f_args = [ ]
for arg in args[1:]:
f_args.append(_prepare_ref(arg, for_names, file_args))
stack.append(['if-any', len(program), f_args, None])
else:
if len(args) > 1:
f_args = [ ]
for arg in args:
f_args.append(_prepare_ref(arg, for_names, file_args))
program.append((self._cmd_format, (f_args[0], f_args[1:])))
else:
program.append((self._cmd_print,
_prepare_ref(args[0], for_names, file_args)))
if stack:
raise UnclosedBlocksError()
return program
def _execute(self, program, fp, ctx):
"""This private helper function takes a 'program' sequence as created
by the method '_parse' and executes it step by step. strings are written
to the file object 'fp' and functions are called.
"""
for step in program:
if isinstance(step, StringType):
fp.write(step)
else:
step[0](step[1], fp, ctx)
def _cmd_print(self, valref, fp, ctx):
value = _get_value(valref, ctx)
if hasattr(value, 'read'):
while 1:
chunk = value.read(16384)
if not chunk:
break
fp.write(chunk)
else:
fp.write(value)
def _cmd_format(self, valref_args, fp, ctx):
(valref, args) = valref_args
fmt = _get_value(valref, ctx)
parts = _re_subst.split(fmt)
for i in range(len(parts)):
piece = parts[i]
if i%2 == 1 and piece != '%':
idx = int(piece)
if idx < len(args):
piece = _get_value(args[idx], ctx)
else:
piece = '<undef>'
fp.write(piece)
def _cmd_include(self, valref_reader, fp, ctx):
(valref, reader) = valref_reader
fname = _get_value(valref, ctx)
self._execute(self._parse(reader.read_other(fname)), fp, ctx)
def _cmd_if_any(self, args, fp, ctx):
"If any value is a non-empty string or non-empty list, then T else F."
(valrefs, t_section, f_section) = args
value = 0
for valref in valrefs:
if _get_value(valref, ctx):
value = 1
break
self._do_if(value, t_section, f_section, fp, ctx)
def _cmd_if_index(self, args, fp, ctx):
((valref, value), t_section, f_section) = args
list, idx = ctx.for_index[valref[0]]
if value == 'even':
value = idx % 2 == 0
elif value == 'odd':
value = idx % 2 == 1
elif value == 'first':
value = idx == 0
elif value == 'last':
value = idx == len(list)-1
else:
value = idx == int(value)
self._do_if(value, t_section, f_section, fp, ctx)
def _cmd_is(self, args, fp, ctx):
((left_ref, right_ref), t_section, f_section) = args
value = _get_value(right_ref, ctx)
value = _get_value(left_ref, ctx).lower() == value.lower()
self._do_if(value, t_section, f_section, fp, ctx)
def _do_if(self, value, t_section, f_section, fp, ctx):
if t_section is None:
t_section = f_section
f_section = None
if value:
section = t_section
else:
section = f_section
if section is not None:
self._execute(section, fp, ctx)
def _cmd_for(self, args, fp, ctx):
((valref,), unused, section) = args
list = _get_value(valref, ctx)
if isinstance(list, StringType):
raise NeedSequenceError()
refname = valref[0]
ctx.for_index[refname] = idx = [ list, 0 ]
for item in list:
self._execute(section, fp, ctx)
idx[1] = idx[1] + 1
del ctx.for_index[refname]
def boolean(value):
"Return a value suitable for [if-any bool_var] usage in a template."
if value:
return 'yes'
return None
def _prepare_ref(refname, for_names, file_args):
"""refname -> a string containing a dotted identifier. example:"foo.bar.bang"
for_names -> a list of active for sequences.
Returns a `value reference', a 3-Tupel made out of (refname, start, rest),
for fast access later.
"""
if refname[0] == '"':
return None, refname[1:-1], None
if refname[:3] == 'arg':
try:
idx = int(refname[3:])
except ValueError:
pass
else:
if idx < len(file_args):
return file_args[idx]
parts = refname.split('.')
start = parts[0]
rest = parts[1:]
while rest and (start in for_names):
name = start + '.' + rest[0]
if name in for_names:
start = name
del rest[0]
else:
break
return refname, start, rest
def _get_value(refname_start_rest, ctx):
"""(refname, start, rest) -> a prepared `value reference' (see above).
ctx -> an execution context instance.
Does a name space lookup within the template name space. Active
for blocks take precedence over data dictionary members with the
same name.
"""
(refname, start, rest) = refname_start_rest
if rest is None:
return start
if start in ctx.for_index:
list, idx = ctx.for_index[start]
ob = list[idx]
elif start in ctx.data:
ob = ctx.data[start]
else:
raise UnknownReference(refname)
for attr in rest:
try:
ob = getattr(ob, attr)
except AttributeError:
raise UnknownReference(refname)
if isinstance(ob, IntType) or isinstance(ob, FloatType):
return str(ob)
if ob is None:
return ''
return ob
class _context:
"""A container for the execution context"""
class Reader:
"Abstract class which allows EZT to detect Reader objects."
class _FileReader(Reader):
"""Reads templates from the filesystem."""
def __init__(self, fname):
self.text = open(fname, 'rb').read()
self._dir = os.path.dirname(fname)
def read_other(self, relative):
return _FileReader(os.path.join(self._dir, relative))
class _TextReader(Reader):
"""'Reads' a template from provided text."""
def __init__(self, text):
self.text = text
def read_other(self, relative):
raise BaseUnavailableError()
class EZTException(Exception):
"""Parent class of all EZT exceptions."""
class ArgCountSyntaxError(EZTException):
"""A bracket directive got the wrong number of arguments."""
class UnknownReference(EZTException):
"""The template references an object not contained in the data dictionary."""
class NeedSequenceError(EZTException):
"""The object dereferenced by the template is no sequence (tuple or list)."""
class UnclosedBlocksError(EZTException):
"""This error may be simply a missing [end]."""
class UnmatchedEndError(EZTException):
"""This error may be caused by a misspelled if directive."""
class BaseUnavailableError(EZTException):
"""Base location is unavailable, which disables includes."""
def test_parse():
assert _re_parse.split('[a]') == ['', '[a]', None, '']
assert _re_parse.split('[a] [b]') == \
['', '[a]', None, ' ', '[b]', None, '']
assert _re_parse.split('[a c] [b]') == \
['', '[a c]', None, ' ', '[b]', None, '']
assert _re_parse.split('x [a] y [b] z') == \
['x ', '[a]', None, ' y ', '[b]', None, ' z']
assert _re_parse.split('[a "b" c "d"]') == \
['', '[a "b" c "d"]', None, '']
assert _re_parse.split(r'["a \"b[foo]" c.d f]') == \
['', '["a \\"b[foo]" c.d f]', None, '']
def _test(argv):
import doctest, ezt
verbose = "-v" in argv
return doctest.testmod(ezt, verbose=verbose)
if __name__ == "__main__":
import sys
sys.exit(_test(sys.argv)[0])