Turn on F401: Unused import warning. (#18598)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18598
ghimport-source-id: c74597e5e7437e94a43c163cee0639b20d0d0c6a

Stack from [ghstack](https://github.com/ezyang/ghstack):
* **#18598 Turn on F401: Unused import warning.**

This was requested by someone at Facebook; this lint is turned
on for Facebook by default.  "Sure, why not."

I had to noqa a number of imports in __init__.  Hypothetically
we're supposed to use __all__ in this case, but I was too lazy
to fix it.  Left for future work.

Be careful!  flake8-2 and flake8-3 behave differently with
respect to import resolution for # type: comments.  flake8-3 will
report an import unused; flake8-2 will not.  For now, I just
noqa'd all these sites.

All the changes were done by hand.

Signed-off-by: Edward Z. Yang <ezyang@fb.com>

Differential Revision: D14687478

fbshipit-source-id: 30d532381e914091aadfa0d2a5a89404819663e3

6 files changed, 7 insertions, 14 deletions

diff --git a/torch/utils/bottleneck/__main__.py b/torch/utils/bottleneck/__main__.py
index ae5de6b9da..0cca3c4b04 100644
--- a/torch/utils/bottleneck/__main__.py
+++ b/torch/utils/bottleneck/__main__.py
@@ -1,11 +1,8 @@
 import argparse
 import cProfile
 import pstats
-import subprocess
 import sys
 import os
-import re
-import contextlib
 
 import torch
 from torch.autograd import profiler
diff --git a/torch/utils/collect_env.py b/torch/utils/collect_env.py
index 9c28124074..2c3f380895 100644
--- a/torch/utils/collect_env.py
+++ b/torch/utils/collect_env.py
@@ -4,8 +4,6 @@ from __future__ import absolute_import, division, print_function, unicode_litera
 import re
 import subprocess
 import sys
-import time
-import datetime
 import os
 from collections import namedtuple
 
diff --git a/torch/utils/data/__init__.py b/torch/utils/data/__init__.py
index ee58707ba3..1852aca404 100644
--- a/torch/utils/data/__init__.py
+++ b/torch/utils/data/__init__.py
@@ -1,4 +1,4 @@
-from .sampler import Sampler, SequentialSampler, RandomSampler, SubsetRandomSampler, WeightedRandomSampler, BatchSampler
-from .distributed import DistributedSampler
-from .dataset import Dataset, TensorDataset, ConcatDataset, Subset, random_split
-from .dataloader import DataLoader
+from .sampler import Sampler, SequentialSampler, RandomSampler, SubsetRandomSampler, WeightedRandomSampler, BatchSampler  # noqa: F401
+from .distributed import DistributedSampler  # noqa: F401
+from .dataset import Dataset, TensorDataset, ConcatDataset, Subset, random_split  # noqa: F401
+from .dataloader import DataLoader  # noqa: F401
diff --git a/torch/utils/data/_utils/__init__.py b/torch/utils/data/_utils/__init__.py
index 05b2b654c6..893b716a0b 100644
--- a/torch/utils/data/_utils/__init__.py
+++ b/torch/utils/data/_utils/__init__.py
@@ -58,4 +58,4 @@ def _set_python_exit_flag():
 atexit.register(_set_python_exit_flag)
 
 
-from . import worker, signal_handling, pin_memory, collate
+from . import worker, signal_handling, pin_memory, collate  # noqa: F401
diff --git a/torch/utils/data/_utils/pin_memory.py b/torch/utils/data/_utils/pin_memory.py
index f762aff315..979044e7a4 100644
--- a/torch/utils/data/_utils/pin_memory.py
+++ b/torch/utils/data/_utils/pin_memory.py
@@ -7,7 +7,7 @@ static methods.
 
 import torch
 from torch._six import queue, container_abcs, string_classes
-from . import collate, MP_STATUS_CHECK_INTERVAL, ExceptionWrapper
+from . import MP_STATUS_CHECK_INTERVAL, ExceptionWrapper
 
 
 def _pin_memory_loop(in_queue, out_queue, device_id, done_event):
diff --git a/torch/utils/data/_utils/signal_handling.py b/torch/utils/data/_utils/signal_handling.py
index 9364733d92..3f8a90e214 100644
--- a/torch/utils/data/_utils/signal_handling.py
+++ b/torch/utils/data/_utils/signal_handling.py
@@ -32,9 +32,7 @@ multiprocessing data loading robust to errors.
 
 import signal
 import threading
-import torch
-from torch._C import _set_worker_pids, _remove_worker_pids, \
-    _error_if_any_worker_fails, _set_worker_signal_handlers
+from torch._C import _set_worker_pids, _remove_worker_pids, _error_if_any_worker_fails, _set_worker_signal_handlers  # noqa: F401
 from . import IS_WINDOWS