A function to guess whether a byte stream contains EBCDIC or ASCII text.

encoding.py

@@ -0,0 +1,42 @@
+COMMON = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789:_- '
+EBCDIC = set(COMMON.encode('cp037'))
+ASCII = set(COMMON.encode('ascii'))
+
+def guess_encoding(bs, threshold=0.5):
+    """Try to determine whether the encoding of byte stream b is an ASCII string or an EBCDIC string.
+
+    Args:
+        bs: A byte string (Python 2 - str; Python 3 - bytes)
+
+    Returns:
+        A string which can be used with the Python encoding functions: 'cp037' for EBCDIC, 'ascii' for ASCII or None
+        if neither.
+    """
+
+    ebcdic_count = 0
+    ascii_count = 0
+
+    count = 0
+    for b in bs:
+        if b in EBCDIC:
+            ebcdic_count +=1
+        if b in ASCII:
+            ascii_count +=1
+        count += 1
+
+    if count == 0:
+        return None
+
+    ebcdic_freq = ebcdic_count / count
+    ascii_freq = ascii_count / count
+
+    if ebcdic_freq < threshold and ascii_freq < threshold:
+        return None
+
+    if ebcdic_freq < threshold and ascii_freq >= threshold:
+        return 'ascii'
+
+    if ebcdic_freq >= threshold and ascii_freq < threshold:
+        return 'cp037'
+
+    return None