Added isfile function for local and s3 file system

csst_fs/__init__.py

@@ -3,3 +3,4 @@ from .fits import fsspec_header
 from .fits import fsspec_HDUList
 from .table import fsspec_table
 from . import s3_fs
+from . import fs
\ No newline at end of file

csst_fs/fs.py

+from .s3_fs import is_s3_path
+from .s3_fs import isfile as s3_isfile
+from .local_fs import isfile as local_isfile
+
+def isfile(path: str, *args, **kwargs) -> bool:
+    if is_s3_path(path):
+        return s3_isfile(path, *args, **kwargs)
+    else:
+        return local_isfile(path, *args, **kwargs)

csst_fs/local_fs.py

+import os
+
+def isfile(path: str) -> bool:
+    return os.path.isfile(path)
+    
\ No newline at end of file

csst_fs/s3_fs.py

@@ -16,3 +16,12 @@ def info(path, bucket=None, key=None, refresh=False, version_id=None, s3_options
 
 def open(file: str, mode: str='r', s3_options=load_s3_options()):
     return open_fileobj(path=file, s3_options=s3_options, mode=mode)
+
+def isfile(path: str, s3_options: dict=load_s3_options()) -> bool:
+    s3_fs = fsspec.filesystem('s3', **s3_options)
+    return s3_fs.isfile(path)
+    
+def is_s3_path(path: str):
+    if(path.startswith("s3")):
+        return True
+    return False