detectron2: ImportError: cannot import name '_C' from 'detectron2'

I had no problem using Densepose. However when I was trying to use PointRend I had this issue. I tried reinstalling but the same thing happened

If you do not know the root cause of the problem / bug, and wish someone to help you, please post according to this template:

Instructions To Reproduce the Issue:

1. what code you wrote

# You may need to restart your runtime prior to this, to let your installation take effect
# Some basic setup:
# Setup detectron2 logger
import detectron2
from detectron2.utils.logger import setup_logger
setup_logger()

# import some common libraries
import numpy as np
import cv2
import torch


# import some common detectron2 utilities
from detectron2 import model_zoo
from detectron2.engine import DefaultPredictor
from detectron2.config import get_cfg
from detectron2.utils.visualizer import Visualizer, ColorMode
from detectron2.data import MetadataCatalog
coco_metadata = MetadataCatalog.get("coco_2017_val")

# import PointRend project
import sys; sys.path.insert(1, "detectron2_repo/projects/PointRend")
import point_rend

im = cv2.imread("frank_front.jpg")
cv2.imshow(im)

1. what exact command you run: I ran the code
2. what you observed (including the full logs):

Traceback (most recent call last):
  File "/home/elysium/detectron2-master/projects/practice.py", line 15, in <module>
    from detectron2 import model_zoo
  File "/home/elysium/detectron2-master/detectron2/model_zoo/__init__.py", line 7, in <module>
    from .model_zoo import get, get_config_file, get_checkpoint_url
  File "/home/elysium/detectron2-master/detectron2/model_zoo/model_zoo.py", line 8, in <module>
    from detectron2.modeling import build_model
  File "/home/elysium/detectron2-master/detectron2/modeling/__init__.py", line 4, in <module>
    from detectron2.layers import ShapeSpec
  File "/home/elysium/detectron2-master/detectron2/layers/__init__.py", line 3, in <module>
    from .deform_conv import DeformConv, ModulatedDeformConv
  File "/home/elysium/detectron2-master/detectron2/layers/deform_conv.py", line 10, in <module>
    from detectron2 import _C
ImportError: cannot import name '_C' from 'detectron2' (/home/elysium/detectron2-master/detectron2/__init__.py)

1. please also simplify the steps as much as possible so they do not require additional resources to run, such as a private dataset.

Expected behavior:

I expected no error

Environment:

Run python -m detectron2.utils.collect_env in the environment where you observerd the issue, and paste the output.

---

sys.platform linux Python 3.7.6 (default, Jan 8 2020, 19:59:22) [GCC 7.3.0] numpy 1.18.1 detectron2._C failed to import DETECTRON2_ENV_MODULE <not set> PyTorch 1.4.0+cu100 @/home/elysium/anaconda3/envs/detectron2-master/lib/python3.7/site-packages/torch PyTorch debug build False CUDA available True GPU 0 GeForce GTX 1070 Ti CUDA_HOME /usr NVCC Cuda compilation tools, release 7.5, V7.5.17 Pillow 7.0.0 torchvision 0.5.0+cu100 @/home/elysium/anaconda3/envs/detectron2-master/lib/python3.7/site-packages/torchvision torchvision arch flags sm_35, sm_50, sm_60, sm_70, sm_75 cv2 4.2.0

---

PyTorch built with:

• GCC 7.3
• Intel® Math Kernel Library Version 2020.0.0 Product Build 20191122 for Intel® 64 architecture applications
• Intel® MKL-DNN v0.21.1 (Git Hash 7d2fd500bc78936d1d648ca713b901012f470dbc)
• OpenMP 201511 (a.k.a. OpenMP 4.5)
• NNPACK is enabled
• CUDA Runtime 10.0
• NVCC architecture flags: -gencode;arch=compute_37,code=sm_37;-gencode;arch=compute_50,code=sm_50;-gencode;arch=compute_60,code=sm_60;-gencode;arch=compute_61,code=sm_61;-gencode;arch=compute_70,code=sm_70;-gencode;arch=compute_75,code=sm_75;-gencode;arch=compute_37,code=compute_37
• CuDNN 7.6.3
• Magma 2.5.1
• Build settings: BLAS=MKL, BUILD_NAMEDTENSOR=OFF, BUILD_TYPE=Release, CXX_FLAGS= -Wno-deprecated -fvisibility-inlines-hidden -fopenmp -DUSE_FBGEMM -DUSE_QNNPACK -DUSE_PYTORCH_QNNPACK -O2 -fPIC -Wno-narrowing -Wall -Wextra -Wno-missing-field-initializers -Wno-type-limits -Wno-array-bounds -Wno-unknown-pragmas -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wno-unused-function -Wno-unused-result -Wno-strict-overflow -Wno-strict-aliasing -Wno-error=deprecated-declarations -Wno-stringop-overflow -Wno-error=pedantic -Wno-error=redundant-decls -Wno-error=old-style-cast -fdiagnostics-color=always -faligned-new -Wno-unused-but-set-variable -Wno-maybe-uninitialized -fno-math-errno -fno-trapping-math -Wno-stringop-overflow, DISABLE_NUMA=1, PERF_WITH_AVX=1, PERF_WITH_AVX2=1, PERF_WITH_AVX512=1, USE_CUDA=ON, USE_EXCEPTION_PTR=1, USE_GFLAGS=OFF, USE_GLOG=OFF, USE_MKL=ON, USE_MKLDNN=ON, USE_MPI=OFF, USE_NCCL=ON, USE_NNPACK=ON, USE_OPENMP=ON, USE_STATIC_DISPATCH=OFF,