WA3 Exsisting Code

wa/utils/serializer.py

@@ -0,0 +1,245 @@
+"""
+This module contains wrappers for Python serialization modules for
+common formats that make it easier to serialize/deserialize WA
+Plain Old Data structures (serilizable WA classes implement 
+``to_pod()``/``from_pod()`` methods for converting between POD 
+structures and Python class instances).
+
+The modifications to standard serilization procedures are:
+
+    - mappings are deserialized as ``OrderedDict``\ 's are than standard
+      Python ``dict``\ 's. This allows for cleaner syntax in certain parts
+      of WA configuration (e.g. values to be written to files can be specified
+      as a dict, and they will be written in the order specified in the config).
+    - regular expressions are automatically encoded/decoded. This allows for
+      configuration values to be transparently specified as strings or regexes
+      in the POD config.
+
+This module exports the "wrapped" versions of serialization libraries,
+and this should be imported and used instead of importing the libraries 
+directly. i.e. ::
+
+    from wa.utils.serializer import yaml
+    pod = yaml.load(fh)
+
+instead of ::
+
+    import yaml
+    pod = yaml.load(fh)
+
+It's also possible to suse the serializer directly::
+
+    from wa.utils import serializer
+    pod = serializer.load(fh)
+
+This can also be used to ``dump()`` POD structures. By default,
+``dump()`` will produce JSON, but ``fmt`` parameter may be used to
+specify an alternative format (``yaml`` or ``python``). ``load()`` will
+use the file extension to guess the format, but ``fmt`` may also be used
+to specify it explicitly.
+
+"""
+import os
+import re
+import sys
+import json as _json
+from collections import OrderedDict
+from datetime import datetime
+
+import yaml as _yaml
+import dateutil.parser
+
+from wa.framework.exception import SerializerSyntaxError
+from wa.utils.types import regex_type
+from wa.utils.misc import isiterable
+
+
+__all__ = [
+    'json',
+    'yaml',
+    'read_pod',
+    'dump',
+    'load',
+]
+
+
+
+class WAJSONEncoder(_json.JSONEncoder):
+
+    def default(self, obj):
+        if hasattr(obj, 'to_pod'):
+            return obj.to_pod()
+        elif isinstance(obj, regex_type):
+            return 'REGEX:{}:{}'.format(obj.flags, obj.pattern)
+        elif isinstance(obj, datetime):
+            return 'DATET:{}'.format(obj.isoformat())
+        else:
+            return _json.JSONEncoder.default(self, obj)
+
+
+class WAJSONDecoder(_json.JSONDecoder):
+
+    def decode(self, s):
+        d = _json.JSONDecoder.decode(self, s)
+
+        def try_parse_object(v):
+            if isinstance(v, basestring) and v.startswith('REGEX:'):
+                _, flags, pattern = v.split(':', 2)
+                return re.compile(pattern, int(flags or 0))
+            elif isinstance(v, basestring) and v.startswith('DATET:'):
+                _, pattern = v.split(':', 1)
+                return dateutil.parser.parse(pattern)
+            else:
+                return v
+
+        def load_objects(d):
+            pairs = []
+            for k, v in d.iteritems():
+                if hasattr(v, 'iteritems'):
+                    pairs.append((k, load_objects(v)))
+                elif isiterable(v):
+                    pairs.append((k, [try_parse_object(i) for i in v]))
+                else:
+                    pairs.append((k, try_parse_object(v)))
+            return OrderedDict(pairs)
+
+        return load_objects(d)
+
+
+class json(object):
+
+    @staticmethod
+    def dump(o, wfh, indent=4, *args, **kwargs):
+        return _json.dump(o, wfh, cls=WAJSONEncoder, indent=indent, *args, **kwargs)
+
+
+    @staticmethod
+    def load(fh, *args, **kwargs):
+        try:
+            return _json.load(fh, cls=WAJSONDecoder, object_pairs_hook=OrderedDict, *args, **kwargs)
+        except ValueError as e:
+            raise SerializerSyntaxError(e.message)
+
+    @staticmethod
+    def loads(s, *args, **kwargs):
+        try:
+            return _json.loads(s, cls=WAJSONDecoder, object_pairs_hook=OrderedDict, *args, **kwargs)
+        except ValueError as e:
+            raise SerializerSyntaxError(e.message)
+
+
+_mapping_tag = _yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG
+_regex_tag = u'tag:wa:regex'
+
+
+def _wa_dict_representer(dumper, data):
+    return dumper.represent_mapping(_mapping_tag, data.iteritems())
+
+
+def _wa_regex_representer(dumper, data):
+    text = '{}:{}'.format(data.flags, data.pattern)
+    return dumper.represent_scalar(_regex_tag, text)
+
+
+def _wa_dict_constructor(loader, node):
+    pairs = loader.construct_pairs(node)
+    seen_keys = set()
+    for k, _ in pairs:
+        if k in seen_keys:
+            raise ValueError('Duplicate entry: {}'.format(k))
+        seen_keys.add(k)
+    return OrderedDict(pairs)
+
+
+def _wa_regex_constructor(loader, node):
+    value = loader.construct_scalar(node)
+    flags, pattern = value.split(':', 1)
+    return re.compile(pattern, int(flags or 0))
+
+
+_yaml.add_representer(OrderedDict, _wa_dict_representer)
+_yaml.add_representer(regex_type, _wa_regex_representer)
+_yaml.add_constructor(_mapping_tag, _wa_dict_constructor)
+_yaml.add_constructor(_regex_tag, _wa_regex_constructor)
+
+
+class yaml(object):
+
+    @staticmethod
+    def dump(o, wfh, *args, **kwargs):
+        return _yaml.dump(o, wfh, *args, **kwargs)
+
+    @staticmethod
+    def load(fh, *args, **kwargs):
+        try:
+            return _yaml.load(fh, *args, **kwargs)
+        except _yaml.YAMLError as e:
+            lineno = None
+            if hasattr(e, 'problem_mark'):
+                lineno = e.problem_mark.line
+            raise SerializerSyntaxError(e.message, lineno)
+
+    loads = load
+
+
+class python(object):
+
+    @staticmethod
+    def dump(o, wfh, *args, **kwargs):
+        raise NotImplementedError()
+
+    @classmethod
+    def load(cls, fh, *args, **kwargs):
+        return cls.loads(fh.read())
+
+    @staticmethod
+    def loads(s, *args, **kwargs):
+        pod = {}
+        try:
+            exec s in pod
+        except SyntaxError as e:
+            raise SerializerSyntaxError(e.message, e.lineno)
+        for k in pod.keys():
+            if k.startswith('__'):
+                del pod[k]
+        return pod
+
+
+def read_pod(source, fmt=None):
+    if isinstance(source, basestring):
+        with open(source) as fh:
+            return _read_pod(fh, fmt)
+    elif hasattr(source, 'read') and (hasattr(sourc, 'name') or fmt):
+        return _read_pod(source, fmt)
+    else:
+        message = 'source must be a path or an open file handle; got {}'
+        raise ValueError(message.format(type(source)))
+
+
+def dump(o, wfh, fmt='json', *args, **kwargs):
+    serializer = {
+                'yaml': yaml,
+                'json': json,
+                'python': python,
+                'py': python,
+            }.get(fmt)
+    if serializer is None:
+        raise ValueError('Unknown serialization format: "{}"'.format(fmt))
+    serializer.dump(o, wfh, *args, **kwargs)
+
+
+def load(s, fmt='json', *args, **kwargs):
+    return read_pod(s, fmt=fmt)
+
+
+def _read_pod(fh, fmt=None):
+    if fmt is None:
+        fmt = os.path.splitext(fh.name)[1].lower().strip('.')
+    if fmt == 'yaml':
+        return yaml.load(fh)
+    elif fmt == 'json':
+        return json.load(fh)
+    elif fmt == 'py':
+        return python.load(fh)
+    else:
+        raise ValueError('Unknown format "{}": {}'.format(fmt, path))