Replace legacy file handling with a context manager. (pyca#5092)

atombrella · alex · reaperhulk · commit f89ce40b621c · 2020-01-12T17:32:21.000-05:00
* Replace legacy file handling with a context manager.

* flake8 fix

Co-authored-by: Alex Gaynor &lt;alex.gaynor@gmail.com&gt;
diff --git a/docs/development/custom-vectors/cast5/generate_cast5.py b/docs/development/custom-vectors/cast5/generate_cast5.py
@@ -23,33 +23,34 @@ def encrypt(mode, key, iv, plaintext):
 
 
 def build_vectors(mode, filename):
-    vector_file = open(filename, "r")
-
     count = 0
     output = []
     key = None
     iv = None
     plaintext = None
-    for line in vector_file:
-        line = line.strip()
-        if line.startswith("KEY"):
-            if count != 0:
-                output.append("CIPHERTEXT = {}".format(
-                    encrypt(mode, key, iv, plaintext))
-                )
-            output.append("\nCOUNT = {}".format(count))
-            count += 1
-            name, key = line.split(" = ")
-            output.append("KEY = {}".format(key))
-        elif line.startswith("IV"):
-            name, iv = line.split(" = ")
-            iv = iv[0:16]
-            output.append("IV = {}".format(iv))
-        elif line.startswith("PLAINTEXT"):
-            name, plaintext = line.split(" = ")
-            output.append("PLAINTEXT = {}".format(plaintext))
 
-    output.append("CIPHERTEXT = {}".format(encrypt(mode, key, iv, plaintext)))
+    with open(filename, "r") as vector_file:
+        for line in vector_file:
+            line = line.strip()
+            if line.startswith("KEY"):
+                if count != 0:
+                    output.append("CIPHERTEXT = {}".format(
+                        encrypt(mode, key, iv, plaintext))
+                    )
+                output.append("\nCOUNT = {}".format(count))
+                count += 1
+                name, key = line.split(" = ")
+                output.append("KEY = {}".format(key))
+            elif line.startswith("IV"):
+                name, iv = line.split(" = ")
+                iv = iv[0:16]
+                output.append("IV = {}".format(iv))
+            elif line.startswith("PLAINTEXT"):
+                name, plaintext = line.split(" = ")
+                output.append("PLAINTEXT = {}".format(plaintext))
+        output.append(
+            "CIPHERTEXT = {}".format(encrypt(mode, key, iv, plaintext))
+        )
     return "\n".join(output)
 
 
