Prevent .open(...) from closing ext. file objects

Fixes #312. Now only closes pdfplumber-created streams, not file objects
passed to pdfplumber.open(...).

pdfplumber/pdf.py

@@ -43,7 +43,10 @@ def __init__(self, stream, pages=None, laparams=None, precision=0.001, password=
     @classmethod
     def open(cls, path_or_fp, **kwargs):
         if isinstance(path_or_fp, (str, pathlib.Path)):
-            return cls(open(path_or_fp, "rb"), **kwargs)
+            fp = open(path_or_fp, "rb")
+            inst = cls(fp, **kwargs)
+            inst.close = fp.close
+            return inst
         else:
             return cls(path_or_fp, **kwargs)
 
@@ -69,7 +72,10 @@ def pages(self):
         return self._pages
 
     def close(self):
-        self.stream.close()
+        """
+        Override this method to execute code on __exit__.
+        """
+        pass
 
     def __enter__(self):
         return self

tests/test_basics.py

@@ -158,6 +158,7 @@ def test_loading_fileobj(self):
         with open(path, "rb") as f:
             with pdfplumber.open(f) as pdf:
                 assert len(pdf.metadata)
+            assert not f.closed
 
         # Will be removed from library soon
         with open(path, "rb") as f: