diff --git a/README.md b/README.md
index 01b9e93..15a6507 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ and checked for integrity by SHA-256 hashes.
 
 ### dependencies
 
-python 3.6 (or later), numpy.
+python 3.5 (or later), numpy.
 
 ### install
 
diff --git a/TODO b/TODO
index 1caefc8..6467f43 100644
--- a/TODO
+++ b/TODO
@@ -4,8 +4,6 @@
 
  *  document prepare() function
 
- *  support python 3.5
-
  *  adjust dates created/modified on server-hosted files to something sensible
 
  *  host files on a more reliable service
@@ -14,6 +12,10 @@
 
  *  basic tests (including running pycodestyle)
 
+ *  --fix (delete corrupt files) and --debug (logging.DEBUG) __main__ arguments
+
+ *  try python 3.2 with an old version of numpy (don't care if it doesn't work)
+
 ### release version 1.0
 
  *  submit to pypi
diff --git a/mnists/__init__.py b/mnists/__init__.py
index cfc9e21..a8a10ef 100644
--- a/mnists/__init__.py
+++ b/mnists/__init__.py
@@ -90,14 +90,15 @@ def validate(name):
     if name not in hashes.keys():
         raise UnknownDatasetError(name)
 
-    with open(construct_path(name), "rb") as f:
+    path = construct_path(name)
+    with open(path, "rb") as f:
         data = f.read()
 
     known_hash = hashes[name]
     hash = hashlib.sha256(data).hexdigest()
 
     if hash != known_hash:
-        raise IntegrityError(file, known_hash, hash)
+        raise IntegrityError(path, known_hash, hash)
 
 
 def onehot(ind):
diff --git a/mnists/__main__.py b/mnists/__main__.py
index a504d4a..df5d379 100644
--- a/mnists/__main__.py
+++ b/mnists/__main__.py
@@ -31,7 +31,7 @@ for name in metadata.keys():
     # print out the shape table for use in the README.
     data = prepare(name)
     prefix = metadata[name][0]
-    row_data = [f"[{prefix}][]"]
+    row_data = ["[{}][]".format(prefix)]
     row_data += [name.replace("_", "\\_")]
     row_data += [str(array.shape) for array in data]
     print(row.format(*row_data))
@@ -39,4 +39,4 @@ for name in metadata.keys():
 print()
 
 for anchor, url in urls.items():
-    print(f"[{anchor}]: {url}")
+    print("[{}]: {}".format(anchor, url))
diff --git a/mnists/exceptions.py b/mnists/exceptions.py
index c5b2b57..5d022be 100644
--- a/mnists/exceptions.py
+++ b/mnists/exceptions.py
@@ -5,9 +5,9 @@ class IntegrityError(Exception):
         self.computed_hash = computed_hash
 
     def __str__(self):
-        return f"""Failed to validate dataset: {name}
+        return """Failed to validate dataset: {self.file}
 Hash mismatch: {self.computed_hash} should be {self.expected_hash}
-Please check your local file for tampering or corruption."""
+Please check your local file for tampering or corruption.""".format(self=self)
 
 
 class UnknownDatasetError(Exception):
@@ -15,4 +15,4 @@ class UnknownDatasetError(Exception):
         self.dataset = dataset
 
     def __str__(self):
-        return f"Unknown mnist-like dataset: {dataset}"
+        return "Unknown mnist-like dataset: {self.dataset}".format(self=self)
diff --git a/setup.py b/setup.py
index 12b9d5f..393fe26 100644
--- a/setup.py
+++ b/setup.py
@@ -22,7 +22,7 @@ setup(
         'Natural Language :: English',
         'Programming Language :: Python',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.5',
         'Topic :: Scientific/Engineering',
     ]
 )