[doc] Check and raise an error if the user is running Python from the…

… parent directory of the sam2 repo

If the user has "sam2/sam2" in their path, they are likey importing the repo itself as "sam2" rather than importing the "sam2" python package (i.e. "sam2/sam2" directory). This typically happens because the user is running Python from the parent directory that contains the sam2 repo they cloned.

In general, the user should not run Python from the parent dir when the repo is cloned into (same is true for e.g. Numpy repo that contains names like `numpy/numpy` where the module and the repo have the same name.

README.md

@@ -26,9 +26,9 @@
 SAM 2 needs to be installed first before use. The code requires `python>=3.10`, as well as `torch>=2.3.1` and `torchvision>=0.18.1`. Please follow the instructions [here](https://pytorch.org/get-started/locally/) to install both PyTorch and TorchVision dependencies. You can install SAM 2 on a GPU machine using:
 
 ```bash
-git clone https://github.com/facebookresearch/sam2.git
+git clone https://github.com/facebookresearch/sam2.git && cd sam2
 
-cd sam2 & pip install -e .
+pip install -e .
 ```
 If you are installing on Windows, it's strongly recommended to use [Windows Subsystem for Linux (WSL)](https://learn.microsoft.com/en-us/windows/wsl/install) with Ubuntu.
 

sam2/build_sam.py

@@ -5,12 +5,31 @@
 # LICENSE file in the root directory of this source tree.
 
 import logging
+import os
 
 import torch
 from hydra import compose
 from hydra.utils import instantiate
 from omegaconf import OmegaConf
 
+import sam2
+
+# Check if the user is running Python from the parent directory of the sam2 repo
+# (i.e. the directory where this repo is cloned into) -- this is not supported since
+# it could shadow the sam2 package and cause issues.
+if os.path.isdir(os.path.join(sam2.__path__[0], "sam2")):
+    # If the user has "sam2/sam2" in their path, they are likey importing the repo itself
+    # as "sam2" rather than importing the "sam2" python package (i.e. "sam2/sam2" directory).
+    # This typically happens because the user is running Python from the parent directory
+    # that contains the sam2 repo they cloned.
+    raise RuntimeError(
+        "You're likely running Python from the parent directory of the sam2 repo "
+        "(i.e. the directory where this repo https://github.com/facebookresearch/sam2 is cloned into). "
+        "This is not supported since the `sam2` package could be shadowed by the repository dir name. "
+        "Please run Python from another directory (e.g. from the repo dir itself rather than its parent, "
+        "or from your home directory) after installing SAM 2."
+    )
+
 HF_MODEL_ID_TO_FILENAMES = {
     "facebook/sam2-hiera-tiny": (
         "configs/sam2/sam2_hiera_t.yaml",