scopes.py

# Copyright 2016 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.
# ==============================================================================
"""Contains the new arg_scope used for TF-Slim ops.

  Allows one to define models much more compactly by eliminating boilerplate
  code. This is accomplished through the use of argument scoping (arg_scope).

  Example of how to use scopes.arg_scope:

  with scopes.arg_scope(ops.conv2d, padding='SAME',
                      stddev=0.01, weight_decay=0.0005):
    net = ops.conv2d(inputs, 64, [11, 11], 4, padding='VALID', scope='conv1')
    net = ops.conv2d(net, 256, [5, 5], scope='conv2')

  The first call to conv2d will overwrite padding:
    ops.conv2d(inputs, 64, [11, 11], 4, padding='VALID',
              stddev=0.01, weight_decay=0.0005, scope='conv1')

  The second call to Conv will use predefined args:
    ops.conv2d(inputs, 256, [5, 5], padding='SAME',
               stddev=0.01, weight_decay=0.0005, scope='conv2')

  Example of how to reuse an arg_scope:
  with scopes.arg_scope(ops.conv2d, padding='SAME',
                      stddev=0.01, weight_decay=0.0005) as conv2d_arg_scope:
    net = ops.conv2d(net, 256, [5, 5], scope='conv1')
    ....

  with scopes.arg_scope(conv2d_arg_scope):
    net = ops.conv2d(net, 256, [5, 5], scope='conv2')

  Example of how to use scopes.add_arg_scope:

  @scopes.add_arg_scope
  def conv2d(*args, **kwargs)
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import contextlib
import functools

from tensorflow.python.framework import ops

_ARGSTACK_KEY = ("__arg_stack",)

_DECORATED_OPS = set()


def _get_arg_stack():
    stack = ops.get_collection(_ARGSTACK_KEY)
    if stack:
        return stack[0]
    else:
        stack = [{}]
        ops.add_to_collection(_ARGSTACK_KEY, stack)
        return stack


def _current_arg_scope():
    stack = _get_arg_stack()
    return stack[-1]


def _add_op(op):
    key_op = (op.__module__, op.__name__)
    if key_op not in _DECORATED_OPS:
        _DECORATED_OPS.add(key_op)


@contextlib.contextmanager
def arg_scope(list_ops_or_scope, **kwargs):
    """Stores the default arguments for the given set of list_ops.

    For usage, please see examples at top of the file.

    Args:
      list_ops_or_scope: List or tuple of operations to set argument scope for or
        a dictionary containg the current scope. When list_ops_or_scope is a dict,
        kwargs must be empty. When list_ops_or_scope is a list or tuple, then
        every op in it need to be decorated with @add_arg_scope to work.
      **kwargs: keyword=value that will define the defaults for each op in
                list_ops. All the ops need to accept the given set of arguments.

    Yields:
      the current_scope, which is a dictionary of {op: {arg: value}}
    Raises:
      TypeError: if list_ops is not a list or a tuple.
      ValueError: if any op in list_ops has not be decorated with @add_arg_scope.
    """
    if isinstance(list_ops_or_scope, dict):
        # Assumes that list_ops_or_scope is a scope that is being reused.
        if kwargs:
            raise ValueError("When attempting to re-use a scope by suppling a"
                             "dictionary, kwargs must be empty.")
        current_scope = list_ops_or_scope.copy()
        try:
            _get_arg_stack().append(current_scope)
            yield current_scope
        finally:
            _get_arg_stack().pop()
    else:
        # Assumes that list_ops_or_scope is a list/tuple of ops with kwargs.
        if not isinstance(list_ops_or_scope, (list, tuple)):
            raise TypeError("list_ops_or_scope must either be a list/tuple or reused"
                            "scope (i.e. dict)")
        try:
            current_scope = _current_arg_scope().copy()
            for op in list_ops_or_scope:
                key_op = (op.__module__, op.__name__)
                if not has_arg_scope(op):
                    raise ValueError("%s is not decorated with @add_arg_scope", key_op)
                if key_op in current_scope:
                    current_kwargs = current_scope[key_op].copy()
                    current_kwargs.update(kwargs)
                    current_scope[key_op] = current_kwargs
                else:
                    current_scope[key_op] = kwargs.copy()
            _get_arg_stack().append(current_scope)
            yield current_scope
        finally:
            _get_arg_stack().pop()


def add_arg_scope(func):
    """Decorates a function with args so it can be used within an arg_scope.

    Args:
      func: function to decorate.

    Returns:
      A tuple with the decorated function func_with_args().
    """

    @functools.wraps(func)
    def func_with_args(*args, **kwargs):
        current_scope = _current_arg_scope()
        current_args = kwargs
        key_func = (func.__module__, func.__name__)
        if key_func in current_scope:
            current_args = current_scope[key_func].copy()
            current_args.update(kwargs)
        return func(*args, **current_args)

    _add_op(func)
    return func_with_args


def has_arg_scope(func):
    """Checks whether a func has been decorated with @add_arg_scope or not.

    Args:
      func: function to check.

    Returns:
      a boolean.
    """
    key_op = (func.__module__, func.__name__)
    return key_op in _DECORATED_OPS