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# Copyright 2015 Google Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Helper functions for commonly used utilities."""
import functools
import inspect
import logging
import warnings
import six
from six.moves import urllib
logger = logging.getLogger(__name__)
POSITIONAL_WARNING = 'WARNING'
POSITIONAL_EXCEPTION = 'EXCEPTION'
POSITIONAL_IGNORE = 'IGNORE'
POSITIONAL_SET = frozenset([POSITIONAL_WARNING, POSITIONAL_EXCEPTION,
POSITIONAL_IGNORE])
positional_parameters_enforcement = POSITIONAL_WARNING
_SYM_LINK_MESSAGE = 'File: {0}: Is a symbolic link.'
_IS_DIR_MESSAGE = '{0}: Is a directory'
_MISSING_FILE_MESSAGE = 'Cannot access {0}: No such file or directory'
def positional(max_positional_args):
"""A decorator to declare that only the first N arguments my be positional.
This decorator makes it easy to support Python 3 style keyword-only
parameters. For example, in Python 3 it is possible to write::
def fn(pos1, *, kwonly1=None, kwonly1=None):
...
All named parameters after ``*`` must be a keyword::
fn(10, 'kw1', 'kw2') # Raises exception.
fn(10, kwonly1='kw1') # Ok.
Example
^^^^^^^
To define a function like above, do::
@positional(1)
def fn(pos1, kwonly1=None, kwonly2=None):
...
If no default value is provided to a keyword argument, it becomes a
required keyword argument::
@positional(0)
def fn(required_kw):
...
This must be called with the keyword parameter::
fn() # Raises exception.
fn(10) # Raises exception.
fn(required_kw=10) # Ok.
When defining instance or class methods always remember to account for
``self`` and ``cls``::
class MyClass(object):
@positional(2)
def my_method(self, pos1, kwonly1=None):
...
@classmethod
@positional(2)
def my_method(cls, pos1, kwonly1=None):
...
The positional decorator behavior is controlled by
``_helpers.positional_parameters_enforcement``, which may be set to
``POSITIONAL_EXCEPTION``, ``POSITIONAL_WARNING`` or
``POSITIONAL_IGNORE`` to raise an exception, log a warning, or do
nothing, respectively, if a declaration is violated.
Args:
max_positional_arguments: Maximum number of positional arguments. All
parameters after the this index must be
keyword only.
Returns:
A decorator that prevents using arguments after max_positional_args
from being used as positional parameters.
Raises:
TypeError: if a key-word only argument is provided as a positional
parameter, but only if
_helpers.positional_parameters_enforcement is set to
POSITIONAL_EXCEPTION.
"""
def positional_decorator(wrapped):
@functools.wraps(wrapped)
def positional_wrapper(*args, **kwargs):
if len(args) > max_positional_args:
plural_s = ''
if max_positional_args != 1:
plural_s = 's'
message = ('{function}() takes at most {args_max} positional '
'argument{plural} ({args_given} given)'.format(
function=wrapped.__name__,
args_max=max_positional_args,
args_given=len(args),
plural=plural_s))
if positional_parameters_enforcement == POSITIONAL_EXCEPTION:
raise TypeError(message)
elif positional_parameters_enforcement == POSITIONAL_WARNING:
logger.warning(message)
return wrapped(*args, **kwargs)
return positional_wrapper
if isinstance(max_positional_args, six.integer_types):
return positional_decorator
else:
args, _, _, defaults = inspect.getargspec(max_positional_args)
return positional(len(args) - len(defaults))(max_positional_args)
def parse_unique_urlencoded(content):
"""Parses unique key-value parameters from urlencoded content.
Args:
content: string, URL-encoded key-value pairs.
Returns:
dict, The key-value pairs from ``content``.
Raises:
ValueError: if one of the keys is repeated.
"""
urlencoded_params = urllib.parse.parse_qs(content)
params = {}
for key, value in six.iteritems(urlencoded_params):
if len(value) != 1:
msg = ('URL-encoded content contains a repeated value:'
'%s -> %s' % (key, ', '.join(value)))
raise ValueError(msg)
params[key] = value[0]
return params
def update_query_params(uri, params):
"""Updates a URI with new query parameters.
If a given key from ``params`` is repeated in the ``uri``, then
the URI will be considered invalid and an error will occur.
If the URI is valid, then each value from ``params`` will
replace the corresponding value in the query parameters (if
it exists).
Args:
uri: string, A valid URI, with potential existing query parameters.
params: dict, A dictionary of query parameters.
Returns:
The same URI but with the new query parameters added.
"""
parts = urllib.parse.urlparse(uri)
query_params = parse_unique_urlencoded(parts.query)
query_params.update(params)
new_query = urllib.parse.urlencode(query_params)
new_parts = parts._replace(query=new_query)
return urllib.parse.urlunparse(new_parts)
def _add_query_parameter(url, name, value):
"""Adds a query parameter to a url.
Replaces the current value if it already exists in the URL.
Args:
url: string, url to add the query parameter to.
name: string, query parameter name.
value: string, query parameter value.
Returns:
Updated query parameter. Does not update the url if value is None.
"""
if value is None:
return url
else:
return update_query_params(url, {name: value})
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