I only changed one line! An unknown error occurred

[junha1125]

1. what changes I made (git diff) or what code I wrote

diff --git a/models/detr.py b/models/detr.py
--- a/models/detr.py
+++ b/models/detr.py

-    num_classes = 20 if args.dataset_file != 'coco' else 91 
+    num_classes = 91 if args.dataset_file = 'coco' else 20 

2. what exact command I run:

python main.py \
	--batch_size 1\
        --no_aux_loss\
        --eval\
        --resume https://dl.fbaipublicfiles.com/detr/detr-r50-e632da11.pth
        --coco_path /workspace/coco 

3. what I observed (including full logs):

Exception has occurred: SyntaxError       (note: full exception trace is shown but execution is paused at: _run_module_as_main)
invalid syntax (detr.py, line 314)
  File "/workspace/models/__init__.py", line 2, in <module>
    from .detr import build
  File "/workspace/main.py", line 20, in <module>
    from models import build_model
  File "/opt/conda/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/opt/conda/lib/python3.7/runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "/opt/conda/lib/python3.7/runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "/opt/conda/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/opt/conda/lib/python3.7/runpy.py", line 193, in _run_module_as_main (Current frame)
    "__main__", mod_spec)

4. Explanation

I just changed a single line of code that had no problem at all in terms of meaning.
But I got an error I wouldn't know.

5. Expected behavior:

No bug, No error.

6. Environment:

I used dockerfile in this repo.
But before building dockerfile, I deleted the torch installation part from requirements.txt
in order to let my envronment have torch-cuda-version

Collecting environment information...
PyTorch version: 1.5.0+cu101
Is debug build: No
CUDA used to build PyTorch: 10.1

OS: Ubuntu 18.04.4 LTS
GCC version: (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
CMake version: Could not collect

Python version: 3.7
Is CUDA available: Yes
CUDA runtime version: Could not collect
GPU models and configuration: GPU 0: GeForce GTX TITAN Black
Nvidia driver version: 460.32.03
cuDNN version: Could not collect

Versions of relevant libraries:
[pip3] numpy==1.18.1
[pip3] torch==1.5.0+cu101
[pip3] torchvision==0.6.0+cu101
[conda] blas                      1.0                         mkl  
[conda] mkl                       2020.2                      256  
[conda] mkl-service               2.3.0            py37he8ac12f_0  
[conda] mkl_fft                   1.3.0            py37h54f3939_0  
[conda] mkl_random                1.1.1            py37h0573a6f_0  
[conda] torch                     1.5.0+cu101              pypi_0    pypi
[conda] torchvision               0.6.0+cu101              pypi_0    pypi

[alcinos]

you wrote num_classes = 91 if args.dataset_file = 'coco' else 20 --> the comparison operator in wrong, in python equality is tested with ==