Modify imghdr.py and write unittest

Lib/imghdr.py

@@ -1,9 +1,11 @@
 """Recognize image file formats based on their first few bytes."""
 
-from os import PathLike
+#from os import PathLike
 
 __all__ = ["what"]
 
+# should replace using FileIO into file
+from io import FileIO
 #-------------------------#
 # Recognize image headers #
 #-------------------------#
@@ -12,8 +14,9 @@ def what(file, h=None):
     f = None
     try:
         if h is None:
-            if isinstance(file, (str, PathLike)):
-                f = open(file, 'rb')
+            # if isinstance(file, (str, PathLike))
+            if isinstance(file, str): # FIXME(corona10): RustPython doesn't support PathLike yet.
+                f = FileIO(file, 'rb')
                 h = f.read(32)
             else:
                 location = file.tell()

tests/snippets/imghdrdata/python.pbm

@@ -0,0 +1,3 @@
+P4
+16 16
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tests/snippets/imghdrdata/python.xbm

@@ -0,0 +1,6 @@
+#define python_width 16
+#define python_height 16
+static char python_bits[] = {
+  0xDF, 0xFE, 0x8F, 0xFD, 0x5F, 0xFB, 0xAB, 0xFE, 0xB5, 0x8D, 0xDA, 0x8F, 
+  0xA5, 0x86, 0xFA, 0x83, 0x1A, 0x80, 0x0D, 0x80, 0x0D, 0x80, 0x0F, 0xE0, 
+  0x0F, 0xF8, 0x0F, 0xF8, 0x0F, 0xFC, 0xFF, 0xFF, };

tests/snippets/test_imghdr.py

@@ -0,0 +1,24 @@
+# unittest for modified imghdr.py
+# Should be replace it into https://github.com/python/cpython/blob/master/Lib/test/test_imghdr.py
+
+import imghdr
+
+TEST_FILES = (
+    #('python.png', 'png'),
+    ('python.gif', 'gif'),
+    ('python.bmp', 'bmp'),
+    ('python.ppm', 'ppm'),
+    ('python.pgm', 'pgm'),
+    ('python.pbm', 'pbm'),
+    ('python.jpg', 'jpeg'),
+    ('python.ras', 'rast'),
+    #('python.sgi', 'rgb'),
+    ('python.tiff', 'tiff'),
+    ('python.xbm', 'xbm'),
+    ('python.webp', 'webp'),
+    ('python.exr', 'exr'),
+)
+
+for fname, expected in TEST_FILES:
+    res = imghdr.what('tests/snippets/imghdrdata/'+fname)
+    assert res == expected