Try to get password from user three times.

IPython/lib/security.py

@@ -1,96 +1,100 b''
 """
 Password generation for the IPython notebook.
 """
 
 import hashlib
 import random
 import getpass
 
 # Length of the salt in nr of hex chars, which implies salt_len * 4
 # bits of randomness.
 salt_len = 12
 
-def passwd(passphrase='', algorithm='sha1'):
+def passwd(passphrase=None, algorithm='sha1'):
     """Generate hashed password and salt for use in notebook configuration.
 
     In the notebook configuration, set `c.NotebookApp.password` to
     the generated string.
 
     Parameters
     ----------
     passphrase : str
         Password to hash.  If unspecified, the user is asked to input
         and verify a password.
     algorithm : str
         Hashing algorithm to use (e.g, 'sha1' or any argument supported
         by :func:`hashlib.new`).
 
     Returns
     -------
     hashed_passphrase : str
         Hashed password, in the format 'hash_algorithm:salt:passphrase_hash'.
 
     Examples
     --------
     In [1]: passwd('mypassword')
     Out[1]: 'sha1:7cf3:b7d6da294ea9592a9480c8f52e63cd42cfb9dd12'
 
     """
-    if not passphrase:
-        p0 = getpass.getpass('Enter password: ')
-        p1 = getpass.getpass('Verify password: ')
-        if (p0 == p1):
-            passphrase = p0
+    if passphrase is None:
+        for i in range(3):
+            p0 = getpass.getpass('Enter password: ')
+            p1 = getpass.getpass('Verify password: ')
+            if p0 == p1:
+                passphrase = p0
+                break
+            else:
+                print('Passwords do not match.')
         else:
-            raise ValueError('Passwords did not match.')
+            raise ValueError('No matching passwords found. Giving up.')
 
     h = hashlib.new(algorithm)
     salt = ('%0' + str(salt_len) + 'x') % random.getrandbits(4 * salt_len)
     h.update(passphrase + salt)
 
     return ':'.join((algorithm, salt, h.hexdigest()))
 
 def passwd_check(hashed_passphrase, passphrase):
     """Verify that a given passphrase matches its hashed version.
 
     Parameters
     ----------
     hashed_passphrase : str
         Hashed password, in the format returned by `passwd`.
     passphrase : str
         Passphrase to validate.
 
     Returns
     -------
     valid : bool
         True if the passphrase matches the hash.
 
     Examples
     --------
     In [1]: from IPython.lib.security import passwd_check
 
     In [2]: passwd_check('sha1:7cf3:b7d6da294ea9592a9480c8f52e63cd42cfb9dd12',
        ...:              'mypassword')
     Out[2]: True
 
     In [3]: passwd_check('sha1:7cf3:b7d6da294ea9592a9480c8f52e63cd42cfb9dd12',
        ...:              'anotherpassword')
     Out[3]: False
 
     """
     try:
         algorithm, salt, pw_digest = hashed_passphrase.split(':', 2)
     except (ValueError, TypeError):
         return False
 
     try:
         h = hashlib.new(algorithm)
     except ValueError:
         return False
 
     if len(pw_digest) == 0 or len(salt) != salt_len:
         return False
 
     h.update(passphrase + salt)
 
     return h.hexdigest() == pw_digest