diff --git a/letsencrypt/client/challenge_util.py b/letsencrypt/client/challenge_util.py
index b5198217d..1338089ab 100644
--- a/letsencrypt/client/challenge_util.py
+++ b/letsencrypt/client/challenge_util.py
@@ -53,7 +53,7 @@ def dvsni_gen_cert(filepath, name, r_b64, nonce, key):
     cert_pem = crypto_util.make_ss_cert(
         key.pem, [nonce + CONFIG.INVALID_EXT, name, ext])
 
-    with open(filepath, 'w') as chall_cert_file:
+    with open(filepath, "w") as chall_cert_file:
         chall_cert_file.write(cert_pem)
 
     return le_util.jose_b64encode(dvsni_s)
@@ -69,7 +69,7 @@ def _dvsni_gen_ext(dvsni_r, dvsni_s):
     :rtype: str
 
     """
-    z_base = hashlib.new('sha256')
+    z_base = hashlib.new("sha256")
     z_base.update(dvsni_r)
     z_base.update(dvsni_s)
 
diff --git a/letsencrypt/client/crypto_util.py b/letsencrypt/client/crypto_util.py
index 13d52c4fb..a2e4d27be 100644
--- a/letsencrypt/client/crypto_util.py
+++ b/letsencrypt/client/crypto_util.py
@@ -102,7 +102,7 @@ def make_csr(key_str, domains):
 
     extstack.push(ext)
     csr.add_extensions(extstack)
-    csr.sign(pubkey, 'sha256')
+    csr.sign(pubkey, "sha256")
     assert csr.verify(pubkey)
     pubkey2 = csr.get_pubkey()
     assert csr.verify(pubkey2)
@@ -156,7 +156,7 @@ def make_key(bits):
     :rtype: str
 
     """
-    return Crypto.PublicKey.RSA.generate(bits).exportKey(format='PEM')
+    return Crypto.PublicKey.RSA.generate(bits).exportKey(format="PEM")
 
 
 def valid_privkey(privkey):
@@ -210,11 +210,11 @@ def make_ss_cert(key_str, domains, not_before=None,
 
     if len(domains) > 1:
         m2_cert.add_ext(M2Crypto.X509.new_extension(
-            'basicConstraints', 'CA:FALSE'))
+            "basicConstraints", "CA:FALSE"))
         m2_cert.add_ext(M2Crypto.X509.new_extension(
-            'subjectAltName', ", ".join(["DNS:%s" % d for d in domains])))
+            "subjectAltName", ", ".join(["DNS:%s" % d for d in domains])))
 
-    m2_cert.sign(pubkey, 'sha256')
+    m2_cert.sign(pubkey, "sha256")
     assert m2_cert.verify(pubkey)
     assert m2_cert.verify()
     # print check_purpose(,0
diff --git a/letsencrypt/client/display.py b/letsencrypt/client/display.py
index 6d76cdfeb..7f2f67a21 100644
--- a/letsencrypt/client/display.py
+++ b/letsencrypt/client/display.py
@@ -85,8 +85,8 @@ class NcursesDisplay(object):
         """Display a Yes/No dialog box
 
         :param str message: message to display to user
-        :param str yes_label: label on the 'yes' button
-        :param str no_label: label on the 'no' button
+        :param str yes_label: label on the "yes" button
+        :param str no_label: label on the "no" button
 
         :returns: if yes_label was selected
         :rtype: bool
@@ -139,7 +139,7 @@ class FileDisplay(object):
         :param str message: Message to display
 
         """
-        side_frame = '-' * 79
+        side_frame = "-" * 79
         lines = message.splitlines()
         fixed_l = []
         for line in lines:
@@ -169,12 +169,12 @@ class FileDisplay(object):
             choices = ["%s - %s" % (c[0], c[1]) for c in choices]
 
         self.outfile.write("\n%s\n" % message)
-        side_frame = '-' * 79
+        side_frame = "-" * 79
         self.outfile.write("%s\n" % side_frame)
 
         for i, choice in enumerate(choices, 1):
             self.outfile.write(textwrap.fill(
-                "%d: %s" % (i, choice), 80) + '\n')
+                "%d: %s" % (i, choice), 80) + "\n")
 
         self.outfile.write("%s\n" % side_frame)
 
@@ -197,7 +197,7 @@ class FileDisplay(object):
         """
         ans = raw_input("%s (Enter c to cancel)\n" % message)
 
-        if ans == 'c' or ans == 'C':
+        if ans == "c" or ans == "C":
             return CANCEL, "-1"
         else:
             return OK, ans
@@ -207,13 +207,13 @@ class FileDisplay(object):
 
         :param str message: question for the user
 
-        :returns: True for 'Yes', False for 'No"
+        :returns: True for "Yes", False for "No"
         :rtype: bool
 
         """
         self.outfile.write("\n%s\n" % textwrap.fill(message, 80))
         ans = raw_input("y/n: ")
-        return ans.startswith('y') or ans.startswith('Y')
+        return ans.startswith("y") or ans.startswith("Y")
 
     def filter_names(self, names):
         """Determine which names the user would like to select from a list.
@@ -252,7 +252,7 @@ class FileDisplay(object):
 
         :returns: tuple of the form (code, selection) where
             code is a display exit code
-            selection is the user's int selection
+            selection is the user"s int selection
         :rtype: tuple
 
         """
@@ -261,7 +261,7 @@ class FileDisplay(object):
         while not valid_ans:
 
             ans = raw_input(input_string)
-            if ans.startswith('c') or ans.startswith('C'):
+            if ans.startswith("c") or ans.startswith("C"):
                 code = CANCEL
                 selection = -1
                 valid_ans = True
diff --git a/letsencrypt/client/recovery_token.py b/letsencrypt/client/recovery_token.py
index bf3bad6e1..2c328a46d 100644
--- a/letsencrypt/client/recovery_token.py
+++ b/letsencrypt/client/recovery_token.py
@@ -75,5 +75,5 @@ class RecoveryToken(object):
         """
         le_util.make_or_verify_dir(self.token_dir, 0o700, os.geteuid())
 
-        with open(os.path.join(self.token_dir, domain), 'w') as token_fd:
+        with open(os.path.join(self.token_dir, domain), "w") as token_fd:
             token_fd.write(str(token))
diff --git a/letsencrypt/client/revoker.py b/letsencrypt/client/revoker.py
index 236533327..d16a4ee46 100644
--- a/letsencrypt/client/revoker.py
+++ b/letsencrypt/client/revoker.py
@@ -32,7 +32,7 @@ class Revoker(object):
 
         """
         cert_der = M2Crypto.X509.load_cert(cert["backup_cert_file"]).as_der()
-        with open(cert["backup_key_file"], 'rU') as backup_key_file:
+        with open(cert["backup_key_file"], "rU") as backup_key_file:
             key = backup_key_file.read()
 
         revocation = self.network.send_and_receive_expected(
@@ -59,7 +59,7 @@ class Revoker(object):
 
         csha1_vhlist = self._get_installed_locations()
 
-        with open(list_file, 'rb') as csvfile:
+        with open(list_file, "rb") as csvfile:
             csvreader = csv.reader(csvfile)
             # idx, orig_cert, orig_key
             for row in csvreader:
@@ -96,7 +96,7 @@ class Revoker(object):
         for (cert_path, _, path) in self.installer.get_all_certs_keys():
             try:
                 cert_sha1 = M2Crypto.X509.load_cert(
-                    cert_path).get_fingerprint(md='sha1')
+                    cert_path).get_fingerprint(md="sha1")
                 if cert_sha1 in csha1_vhlist:
                     csha1_vhlist[cert_sha1].append(path)
                 else:
@@ -136,10 +136,10 @@ class Revoker(object):
         list_file = os.path.join(CONFIG.CERT_KEY_BACKUP, "LIST")
         list_file2 = os.path.join(CONFIG.CERT_KEY_BACKUP, "LIST.tmp")
 
-        with open(list_file, 'rb') as orgfile:
+        with open(list_file, "rb") as orgfile:
             csvreader = csv.reader(orgfile)
 
-            with open(list_file2, 'wb') as newfile:
+            with open(list_file2, "wb") as newfile:
                 csvwriter = csv.writer(newfile)
 
                 for row in csvreader:
@@ -274,16 +274,16 @@ class Cert(object):
             status = DELETED_MSG
         else:
             o_cert = M2Crypto.X509.load_cert(orig)
-            if self.get_fingerprint() != o_cert.get_fingerprint(md='sha1'):
+            if self.get_fingerprint() != o_cert.get_fingerprint(md="sha1"):
                 status = CHANGED_MSG
 
         # Verify original key path
         if not os.path.isfile(orig_key):
             key_status = DELETED_MSG
         else:
-            with open(orig_key, 'r') as fd:
+            with open(orig_key, "r") as fd:
                 key_pem = fd.read()
-            with open(backup_key, 'r') as fd:
+            with open(backup_key, "r") as fd:
                 backup_key_pem = fd.read()
             if key_pem != backup_key_pem:
                 key_status = CHANGED_MSG
@@ -307,7 +307,7 @@ class Cert(object):
         return self.cert.get_issuer().as_text()
 
     def get_fingerprint(self):
-        return self.cert.get_fingerprint(md='sha1')
+        return self.cert.get_fingerprint(md="sha1")
 
     def get_not_before(self):
         return self.cert.get_not_before().get_datetime()
diff --git a/letsencrypt/client/tests/client_test.py b/letsencrypt/client/tests/client_test.py
index 5961b227e..a7d4d1148 100644
--- a/letsencrypt/client/tests/client_test.py
+++ b/letsencrypt/client/tests/client_test.py
@@ -84,5 +84,5 @@ class RollbackTest(unittest.TestCase):
         self._call(1)
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     unittest.main()
diff --git a/letsencrypt/client/tests/recovery_token_test.py b/letsencrypt/client/tests/recovery_token_test.py
index 44905789d..5c419da39 100644
--- a/letsencrypt/client/tests/recovery_token_test.py
+++ b/letsencrypt/client/tests/recovery_token_test.py
@@ -60,5 +60,5 @@ class RecoveryTokenTest(unittest.TestCase):
         self.assertTrue(response is None)
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     unittest.main()
diff --git a/letsencrypt/scripts/main.py b/letsencrypt/scripts/main.py
index ae623b640..4f78de968 100755
--- a/letsencrypt/scripts/main.py
+++ b/letsencrypt/scripts/main.py
@@ -134,7 +134,7 @@ def main():  # pylint: disable=too-many-statements,too-many-branches
 
 def display_eula():
     """Displays the end user agreement."""
-    with open('EULA') as eula_file:
+    with open("EULA") as eula_file:
         if not zope.component.getUtility(interfaces.IDisplay).yesno(
                 eula_file.read(), "Agree", "Cancel"):
             sys.exit(0)
@@ -190,7 +190,7 @@ def read_file(filename):
 
     """
     try:
-        return filename, open(filename, 'rU').read()
+        return filename, open(filename, "rU").read()
     except IOError as exc:
         raise argparse.ArgumentTypeError(exc.strerror)