def begin(self, max_steps=None):
    "Called at the beginning of training.\n\n    When called, the default graph is the one we are executing.\n\n    Args:\n      max_steps: `int`, the maximum global step this training will run until.\n\n    Raises:\n      ValueError: if we've already begun a run.\n    "
    if self._begun:
        raise ValueError('begin called twice without end.')
    self._max_steps = max_steps
    self._begun = True
Called at the beginning of training.

When called, the default graph is the one we are executing.

Args:
  max_steps: `int`, the maximum global step this training will run until.

Raises:
  ValueError: if we've already begun a run.
def begin(self, max_steps=None):
    "Called at the beginning of training.\n\n    When called, the default graph is the one we are executing.\n\n    Args:\n      max_steps: `int`, the maximum global step this training will run until.\n\n    Raises:\n      ValueError: if we've already begun a run.\n    "
    if self._begun:
        raise ValueError('begin called twice without end.')
    self._max_steps = max_steps
    self._begun = True