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POSQLAlchemy & PassLib
 

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    <p><strong><em>tl;dr -- How do I use a Python-side library such as PassLib to hash passwords before inserting them into a MySQL DB with SQLAlchemy?</em></strong> </p> <p>Alright, so I've been banging my head on my desk for a day or two trying to figure this out, so here it goes:</p> <p>I am writing a web application using Pyramid/SQLAlchemy and I'm trying to interface with my MySQL database's Users table. </p> <p>Ultimately, I want to do something like the following:</p> <p>Compare a password to the hash: </p> <pre class="lang-python prettyprint-override"><code>if user1.password == 'supersecret' </code></pre> <p>Insert a new password:</p> <pre class="lang-python prettyprint-override"><code>user2.password = 'supersecret' </code></pre> <p>I'd like to be able to use PassLib to hash my passwords before they go to the database, and I'm not really a fan of using the built-in MySQL SHA2 function since it's not salted.</p> <p>However, just to try it, I do have this working using the SQL-side function:</p> <pre class="lang-python prettyprint-override"><code>from sqlalchemy import func, TypeDecorator, type_coerce from sqlalchemy.dialects.mysql import CHAR, VARCHAR, INTEGER from sqlalchemy.ext.declarative import declarative_base from sqlalchemy import Column class SHA2Password(TypeDecorator): """Applies the SHA2 function to incoming passwords.""" impl = CHAR(64) def bind_expression(self, bindvalue): return func.sha2(bindvalue, 256) class comparator_factory(CHAR.comparator_factory): def __eq__(self, other): local_pw = type_coerce(self.expr, CHAR) return local_pw == func.sha2(other, 256) class User(Base): __tablename__ = 'Users' _id = Column('userID', INTEGER(unsigned=True), primary_key=True) username = Column(VARCHAR(length=64)) password = Column(SHA2Password(length=64)) def __init__(self, username, password): self.username = username self.password = password </code></pre> <p>This was copied from the example 2 at <a href="http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DatabaseCrypt" rel="nofollow noreferrer">http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DatabaseCrypt</a></p> <p>So that works and allows me to use the built-in MySQL SHA2 function (by calling <code>func.sha2()</code>) and do exactly what I want. However, now I'm trying to replace this with PassLib on the Python side. </p> <p>PassLib presents two functions: one to create a new password hash, and one to verify a password:</p> <pre class="lang-python prettyprint-override"><code>from passlib.hash import sha256_crypt new_password = sha256_crypt.encrypt("supersecret") sha256_crypt.verify("supersecret", new_password) </code></pre> <p>I can't quite figure out how to actually implement this. Having read all the documentation, I think it is either a different form of TypeDecorator, a custom type declaration, a hybrid value, or a hybrid property. I tried following <a href="https://stackoverflow.com/questions/12212636/sql-alchemy-overriding">this</a>, but it doesn't really make sense to me nor does the code suggested there actually run.</p> <p>So, to sum up my question -- how do I overload the <code>=</code> and <code>==</code> operators so that they run things through the appropriate hash functions?</p>
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