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GeezerVison is showing github.com — fullstackpython.com/object-relational-mappers-orms.html at gh-pages · yu66s/fullstackpython.com Expand file tree/ Copy pathobject-relational-mappers-orms.htmlMore file actions 503 lines (497 loc) · 40.3 KB / Copy pathobject-relational-mappers-orms.htmlFile metadata and controls503 lines (497 loc) · 40.3 KB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 <!DOCTYPE html> <html lang="en"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta name="author" content="Matt Makai"> <meta name="description" content="Object-relational mappers (ORMs) bridge relational databases and object-oriented code. Learn more on Full Stack Python."> <link rel="shortcut icon" href="/img/fsp-fav.png"> <title>Object-relational Mappers (ORMs) - Full Stack Python</title> <!--[if lt IE 9]> <script src="https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js"></script> <script src="https://oss.maxcdn.com/libs/respond.js/1.3.0/respond.min.js"></script> <![endif]--> <link href="theme/css/f.min.css" rel="stylesheet"> </head> <body> <div style="padding: 0 0 20px 0; margin: 0 0 20px 0; background-color: #22B24C;"> <div class="container"> <p class="banner"><a href="https://www.gumroad.com/l/python-deployments" style="color: #fff">Learning web development? Check out The Full Stack Python Guide to Deployments book</a>!</p> </div> </div> <a href="https://github.com/makaimc/fullstackpython.com"><img style="position: absolute; top: 0; right: 0; border: 0;" src="/img/fork.png" alt="Fork me on GitHub"></a> <div class="container"> <div class="row"> <div class="col-md-12"> <div class="logo-header-section"> <a href="/" style="text-decoration: none; border: none;"><img src="theme/img/logo.png" height="52" width="52" class="logo-image" style="padding-top: 1px;" alt="Full Stack Python logo"></a> <span class="logo-title"><a href="/">Full Stack Python</a></span> </div> <div class="subnav"> <!--<a href="/blog.html" class="submenu-item-first">Blog</a> | <a href="/books.html" class="submenu-item">Books</a> | --> <a href="/table-of-contents.html" class="submenu-item-first">Table of contents</a> | <a href="/email.html" class="submenu-item">Email newsletter</a> | <a href="https://twitter.com/fullstackpython" class="submenu-item">@fullstackpython</a> | <a href="https://github.com/makaimc/fullstackpython.com/tree/gh-pages/source" class="submenu-item">Source code</a> </div> </div> </div><div class="row"> <div class="col-md-8"> <h1>Object-relational mappers (ORMs)</h1> <p>An object-relational mapper (ORM) is a code library that automates the transfer of data stored in relational databases tables into objects that are more commonly used in application code.</p> <h2>Why are ORMs useful?</h2> <p>ORMs provide a high-level abstraction upon a <a href="/databases.html">relational database</a> that allows a developer to write Python code instead of SQL to create, read, update and delete data and schemas in their database. Developers can use the programming language they are comfortable with to work with a database instead of writing SQL statements or stored procedures.</p> <p>For example, without an ORM a developer would write the following SQL statement to retrieve every row in the USERS table where the <code>zip_code</code> column is 94107:</p> <div class="highlight"><pre>SELECT * FROM USERS WHERE zip_code=94107; </pre></div> <p>The equivalent Django ORM query would instead look like the following Python code:</p> <div class="highlight"><pre># obtain everyone in the 94107 zip code and assign to users variable users = Users.objects.filter(zip_code=94107) </pre></div> <p>The ability to write Python code instead of SQL can speed up web application development, especially at the beginning of a project. The potential development speed boost comes from not having to switch from Python code into writing declarative paradigm SQL statements. While some software developers may not mind switching back and forth between languages, it's typically easier to knock out a prototype or start a web application using a single programming language.</p> <p>ORMs also make it theoretically possible to switch an application between various relational databases. For example, a developer could use <a href="/sqlite.html">SQLite</a> for local development and <a href="/mysql.html">MySQL</a> in production. A production application could be switched from MySQL to <a href="/postgresql.html">PostgreSQL</a> with minimal code modifications.</p> <p>In practice however, it's best to use the same database for local development as is used in production. Otherwise unexpected errors could hit in production that were not seen in a local development environment. Also, it's rare that a project would switch from one database in production to another one unless there was a pressing reason.</p> <div class="well see-also">While you're learning about ORMs you should also read up on <a href="/deployment.html">deployment</a> and check out the <a href="/application-dependencies.html">application dependencies</a> page.</div> <h2>Do I have to use an ORM for my web application?</h2> <p>Python ORM libraries are not required for accessing relational databases. In fact, the low-level access is typically provided by another library called a <em>database connector</em>, such as <a href="http://initd.org/psycopg/">psycopg</a> (for PostgreSQL) or <a href="https://pypi.python.org/pypi/MySQL-python/1.2.5">MySQL-python</a> (for MySQL). Take a look at the table below which shows how ORMs can work with different web frameworks and connectors and relational databases.</p> <p><img src="/img/orm-examples.png" width="100%" alt="Examples of how varying Python ORMs can work with different connectors and backends." class="technical-diagram" /></p> <p>The above table shows for example that SQLAlchemy can work with varying web frameworks and database connectors. Developers can also use ORMs without a web framework, such as when creating a data analysis tool or a batch script without a user interface.</p> <h2>What are the downsides of using an ORM?</h2> <p>There are numerous downsides of ORMs, including</p> <ol> <li>Impedance mismatch</li> <li>Potential for reduced performance</li> <li>Shifting complexity from the database into the application code</li> </ol> <h3>Impedance mismatch</h3> <p>The phrase "impedance mismatch" is commonly used in conjunction with ORMs. Impedance mismatch is a catch-all term for the difficulties that occur when moving data between relational tables and application objects. The gist is that the way a developer uses objects is different from how data is stored and joined in relational tables.</p> <p><a href="http://www.agiledata.org/essays/impedanceMismatch.html">This article on ORM impedance mismatch</a> does a solid job of explaing what the concept is at a high level and provides diagrams to visualize why the problem occurs.</p> <h3>Potential for reduced performance</h3> <p>One of the concerns that's associated with any higher-level abstraction or framework is potential for reduced performance. With ORMs, the performance hit comes from the translation of application code into a corresponding SQL statement which may not be tuned properly.</p> <p>ORMs are also often easy to try but difficult to master. For example, a beginner using Django might not know about the <a href="https://docs.djangoproject.com/en/1.8/ref/models/querysets/#select-related"><code>select_related()</code> function</a> and how it can improve some queries' foreign key relationship performance. There are dozens of performance tips and tricks for every ORM. It's possible that investing time in learning those quirks may be better spent just learning SQL and how to write stored procedures.</p> <p>There's a lot of hand-waving "may or may not" and "potential for" in this section. In large projects ORMs are good enough for roughly 80-90% of use cases but in 10-20% of a project's database interactions there can be major performance improvements by having a knowledgeable database administrator write tuned SQL statements to replace the ORM's generated SQL code.</p> <h3>Shifting complexity from the database into the app code</h3> <p>The code for working with an application's data has to live somewhere. Before ORMs were common, database stored procedures were used to encapsulate the database logic. With an ORM, the data manipulation code instead lives within the application's Python codebase. The addition of data handling logic in the codebase generally isn't an issue with a sound application design, but it does increase the total amount of Python code instead of splitting code between the application and the database stored procedures.</p> <h2>Python ORM Implementations</h2> <p>There are numerous ORM implementations written in Python, including</p> <ol> <li><a href="https://docs.djangoproject.com/en/1.8/topics/db/">The Django ORM</a></li> <li><a href="http://www.sqlalchemy.org/">SQLAlchemy</a></li> <li><a href="https://peewee.readthedocs.org/en/latest/">Peewee</a></li> <li><a href="http://ponyorm.com/">PonyORM</a></li> <li><a href="http://sqlobject.org/">SQLObject</a></li> </ol> <p>There are other ORMs, such as Canonical's <a href="https://storm.canonical.com/">Storm</a>, but most of them do not appear to currently be under active development. Learn more about the major active ORMs below.</p> <h3>Django's ORM</h3> <p>The <a href="/django.html">Django</a> web framework comes with its own built-in object-relational mapping module, generally referred to as "the Django ORM" or "Django's ORM".</p> <p><a href="https://docs.djangoproject.com/en/dev/topics/db/">Django's ORM</a> works well for simple and medium-complexity database operations. However, there are often complaints that the ORM makes complex queries much more complicated than writing straight SQL or using <a href="http://www.sqlalchemy.org/">SQLAlchemy</a>.</p> <p>It's technically possible to drop down to SQL but it ties the queries to a specific database implementation. The ORM is coupled closely with Django so replacing the default ORM with SQLAlchemy is currently a hack workaround. Note though that some of the Django core committers believe it is only a matter of time before the default ORM is replaced with SQLAlchemy. It will be a large effort to get that working though so it's likely to come in <a href="https://github.com/makaimc/fullstackpython.com/issues/48">Django 1.9 or later</a>.</p> <p>Since the majority of Django projects are tied to the default ORM, it's best to read up on advanced use cases and tools for doing your best work within the existing framework.</p> <h3>SQLAlchemy</h3> <p><a href="http://www.sqlalchemy.org/">SQLAlchemy</a> is a well-regarded Python ORM because it gets the abstraction level "just right" and seems to make complex database queries easier to write than the Django ORM in most cases. SQLAlchemy is typically used with Flask as the database ORM via the <a href="https://pythonhosted.org/Flask-SQLAlchemy/">Flask-SQLAlchemy</a> extension.</p> <h3>Peewee</h3> <p><a href="https://peewee.readthedocs.org/en/latest/">Peewee</a> is a Python ORM written to be "<a href="http://charlesleifer.com/blog/the-case-for-peewee-small-hackable-and-fun/">simpler, smaller and more hackable</a>" than SQLAlchemy. The analogy used by the core Peewee author is that Peewee is to SQLAlchemy as SQLite is to PostgreSQL. An ORM does not have to work for every exhaustive use case in order to be useful.</p> <h3>Pony</h3> <p><a href="http://ponyorm.com/">Pony ORM</a> is another Python ORM with a slight twist in its licensing model. The project is multi-licensed. Pony is free for use on open source projects but has a <a href="http://ponyorm.com/license-and-pricing.html">commercial license</a> that is required for commercial projects. The license is a one-time payment and does not necessitate a recurring fee.</p> <h3>SQLObject</h3> <p><a href="http://sqlobject.org/">SQLObject</a> is an ORM that has been under active open source development since <a href="http://sqlobject.org/News1.html#sqlobject-0-5">before 2003</a>.</p> <h2>Schema migrations</h2> <p>Schema migrations, for example when you need to add a new column to an existing table in your database, are not technically part of ORMs. However, since ORMs typically lead to a hands-off approach to the database (at the developers peril in many cases), libraries to perform schema migrations often go hand-in-hand with Python ORM usage on web application projects.</p> <p>Database schema migrations are a complex topic and deserve their own page. For now, we'll lump schema migration resources under ORM links below.</p> <h3>General ORM resources</h3> <ul> <li> <p>There's also a detailed overview of <a href="http://www.agiledata.org/essays/mappingObjects.html">what ORMs are</a> on another page of the website.</p> </li> <li> <p>This <a href="https://github.com/sloria/PythonORMSleepy">example GitHub project</a> implements the same Flask application with several different ORMs: SQLAlchemy, Peewee, MongoEngine, stdnet and PonyORM.</p> </li> <li> <p>Martin Fowler addresses the <a href="http://martinfowler.com/bliki/OrmHate.html">ORM hate</a> in an essay about how ORMs are often misused but that they do provide benefits to developers.</p> </li> <li> <p>If you're confused about the difference between a connector, such as MySQL-python and an ORM like SQLAlchemy, read this <a href="http://stackoverflow.com/questions/2550292/purpose-of-sqlalchemy-over-mysqldb">StackOverflow answer</a> on the topic.</p> </li> </ul> <h3>Django ORM resources</h3> <ul> <li> <p><a href="http://www.dabapps.com/blog/django-models-and-encapsulation/">Django models, encapsulation and data integrity</a> is a detailed article by Tom Christie on encapsulating Django models for data integrity.</p> </li> <li> <p><a href="http://django-debug-toolbar.readthedocs.org/en/1.2/">Django Debug Toolbar</a> is a powerful Django ORM database query inspection tool. Highly recommended during development to ensure you're writing reasonable query code. <a href="http://mtford.co.uk/blog/2/">Django Silk</a> is another inspection tool and has capabilities to do more than just SQL inspection.</p> </li> <li> <p><a href="http://reinout.vanrees.org/weblog/2014/05/06/making-faster.html">Making a specific Django app faster</a> is a Django performance blog post with some tips on measuring performance and optimizing based on the measured results.</p> </li> <li> <p><a href="https://speakerdeck.com/alex/why-i-hate-the-django-orm">Why I Hate the Django ORM</a> is Alex Gaynor's overview of the bad designs decisions, some of which he made, while building the Django ORM.</p> </li> <li> <p><a href="https://speakerdeck.com/craigkerstiens/going-beyond-django-orm-with-postgres">Going Beyond Django ORM with Postgres</a> is specific to using PostgreSQL with Django.</p> </li> <li> <p><a href="http://www.calazan.com/migrating-django-app-from-mysql-to-postgresql/">Migrating a Django app from MySQL to PostgreSQL</a> is a quick look at how to move from MySQL to PostgreSQL. However, my guess is that any Django app that's been running for awhile on one <a href="/databases.html">relational database</a> will require a lot more work to port over to another backend even with the power of the ORM.</p> </li> <li> <p><a href="http://blog.kevinastone.com/django-model-descriptors.html">Django Model Descriptors</a> discusses and shows how to incorporate business logic into Django models to reduce complexity from the views and make the code easier to reuse across separate views.</p> </li> <li> <p><a href="http://treyhunner.com/2014/03/migrating-to-django-1-dot-7/">Supporting both Django 1.7 and South</a> explains the difficulty of supporting Django 1.7 and maintaining South migrations for Django 1.6 then goes into how it can be done.</p> </li> <li> <p><a href="https://www.calazan.com/adding-basic-search-to-your-django-site/">Adding basic search to your Django site</a> shows how to write generic queries that'll allow you to provide site search via the Django ORM without relying on another tool like ElasticSearch. This is great for small sites before you scale them up with a more robust search engine.</p> </li> <li> <p><a href="https://www.wellfireinteractive.com/blog/using-django-proxy-models">How to use Django's Proxy Models</a> is a solid post on a Django ORM concept that doesn't frequently get a lot of love or explanation.</p> </li> <li> <p><a href="http://tech.marksblogg.com/django-admin-logins.html">Tightening Django Admin Logins</a> shows you how to log authentication failures, create an IP addresses white list and combine fail2ban with the authentication failures list.</p> </li> <li> <p><a href="https://realpython.com/blog/python/django-migrations-a-primer/">Django Migrations - a Primer</a> takes you through the new migrations system integrated in the Django core as of Django 1.7, looking specifically at a solid workflow that you can use for creating and applying migrations.</p> </li> <li> <p><a href="https://markusholtermann.eu/2014/09/django-17-database-migrations-done-right/">Django 1.7: Database Migrations Done Right</a> explains why South was not directly integrated into Django, how migrations are built and shows how backwards migrations work.</p> </li> <li> <p><a href="http://www.rkblog.rk.edu.pl/w/p/squashing-and-optimizing-migrations-django/">Squashing and optimizing migrations in Django</a> shows a simple example with code for how to use the migrations integrated into Django 1.7.</p> </li> <li> <p><a href="https://www.isotoma.com/blog/2015/11/23/sorting-querysets-with-nulls-in-django/">Sorting querysets with NULLs in Django</a> shows what to do if you're struggling with the common issue of sorting columns that contain NULL values.</p> </li> </ul> <h3>SQLAlchemy resources</h3> <ul> <li> <p>If you're interested in the differences between SQLAlchemy and the Django ORM I recommend reading <a href="http://lucumr.pocoo.org/2011/7/19/sqlachemy-and-you/">SQLAlchemy and You</a> by Armin Ronacher.</p> </li> <li> <p>There is an entire chapter in the <a href="http://aosabook.org/en/sqlalchemy.html">Architecture of Open Source Applications book on SQLAlchemy </a>. The content is detailed and well worth reading to understand what's happening under the covers.</p> </li> <li> <p><a href="http://www.pythoncentral.io/sqlalchemy-vs-orms/">SQLAlchemy vs Other ORMs</a> provides a detailed comparison of SQLAlchemy against alternatives.</p> </li> <li> <p>Most Flask developers use SQLAlchemy as an ORM to relational databases. If you're unfamiliar with SQLAlchemy questions will often come up such as <a href="http://stackoverflow.com/questions/4201455/sqlalchemy-whats-the-difference-between-flush-and-commit">what's the difference between flush and commit?</a> that are important to understand as you build out your app.</p> </li> </ul> <h3>Peewee resources</h3> <ul> <li> <p><a href="http://charlesleifer.com/blog/managing-database-connections-with-peewee/">Managing database connections with Peewee</a> explains the connection pool and ExecutionContext of the ORM.</p> </li> <li> <p><a href="http://charlesleifer.com/blog/dear-diary-an-encrypted-command-line-diary-with-python/">An encrypted command-line diary with Python</a> is an awesome walkthrough explaining how to use SQLite, SQLCipher and Peewee to create an encrypted file with your contents, diary or otherwise.</p> </li> <li> <p>The <a href="http://docs.peewee-orm.com/en/latest/peewee/quickstart.html">official Peewee quickstart documentation</a> along with the <a href="http://docs.peewee-orm.com/en/latest/peewee/example.html">example Twitter clone app</a> will walk you through the ins and outs of your first couple Peewee-powered projects.</p> </li> <li> <p><a href="http://charlesleifer.com/blog/shortcomings-in-the-django-orm-and-a-look-at-peewee-a-lightweight-alternative/">Shortcomings in the Django ORM and a look at Peewee</a> from the author of the Peewee ORM explains how some of the design decisions made in Peewee were in reaction to parts of the Django ORM that didn't work so well in practice.</p> </li> <li> <p><a href="http://charlesleifer.com/blog/how-to-make-a-flask-blog-in-one-hour-or-less/">How to make a Flask blog in one hour or less</a> is a well written tutorial that uses the <a href="https://peewee.readthedocs.org/en/latest/">Peewee ORM</a> instead of SQLAlchemy for the blog back end.</p> </li> </ul> <h3>Pony ORM resources</h3> <ul> <li> <p><a href="http://jakeaustwick.me/why-you-should-give-ponyorm-a-chance/">Why you should give Pony ORM a chance</a> explains some of the benefits of Pony ORM that make it worth trying out.</p> </li> <li> <p><a href="http://www.blog.pythonlibrary.org/2014/07/21/python-101-an-intro-to-pony-orm/">An intro to Pony ORM</a> shows the basics of how to use the library, such as creating databases and manipulating data.</p> </li> <li> <p>The Pony ORM author explains on a Stack Overflow answer <a href="http://stackoverflow.com/questions/16115713/how-pony-orm-does-its-tricks">how Pony ORM works behind the scenes</a>. Worth a read whether or not you're using the ORM just to find out how some of the magic coding works.</p> </li> </ul> <h3>SQLObject resources</h3> <ul> <li> <p>This post on <a href="http://www.andypatterns.com/index.php/blog/object_relational_mapping_pattern_-_using_sqlobj/">Object-Relational Mapping with SQLObject</a> explains the concept behind ORMs and shows the Python code for how they can be used.</p> </li> <li> <p>Ian Bicking presented on SQLObject back in 2004 with a talk on <a href="http://www.ianbicking.org/docs/sqlobject-presentation/sqlobject-and-database-programming.html">SQLObject and Database Programming in Python</a>.</p> </li> </ul> <h3>What would you like to learn about building Python web apps?</h3> <div class="row"> <div class="col-md-4"> <div class="well select-next"> <a href="/databases.html" class="btn btn-success btn-full"><svg width="28" height="30" viewBox="0 0 1792 1792" xmlns="http://www.w3.org/2000/svg"><path d="M1168 1216q0 33-23.5 56.5t-56.5 23.5-56.5-23.5-23.5-56.5 23.5-56.5 56.5-23.5 56.5 23.5 23.5 56.5zm256 0q0 33-23.5 56.5t-56.5 23.5-56.5-23.5-23.5-56.5 23.5-56.5 56.5-23.5 56.5 23.5 23.5 56.5zm112 160v-320q0-13-9.5-22.5t-22.5-9.5h-1216q-13 0-22.5 9.5t-9.5 22.5v320q0 13 9.5 22.5t22.5 9.5h1216q13 0 22.5-9.5t9.5-22.5zm-1230-480h1180l-157-482q-4-13-16-21.5t-26-8.5h-782q-14 0-26 8.5t-16 21.5zm1358 160v320q0 66-47 113t-113 47h-1216q-66 0-113-47t-47-113v-320q0-25 16-75l197-606q17-53 63-86t101-33h782q55 0 101 33t63 86l197 606q16 50 16 75z" fill="#fff"/></svg></a> <p class="under-btn">Tell me about standard relational databases.</p> </div> </div> <div class="col-md-4"> <div class="well select-next"> <a href="/no-sql-datastore.html" class="btn btn-success btn-full"><svg width="34" height="30" viewBox="0 0 1792 1792" xmlns="http://www.w3.org/2000/svg"><path d="M1151 960h316q-1-3-2.5-8t-2.5-8l-212-496h-708l-212 496q-1 2-2.5 8t-2.5 8h316l95 192h320zm513 30v482q0 26-19 45t-45 19h-1408q-26 0-45-19t-19-45v-482q0-62 25-123l238-552q10-25 36.5-42t52.5-17h832q26 0 52.5 17t36.5 42l238 552q25 61 25 123z" fill="#fff"/></svg></a> <p class="under-btn">What're these NoSQL data stores hipster developers keep talking about?</p> </div> </div> <div class="col-md-4"> <div class="well select-next"> <a href="/data.html" class="btn btn-success btn-full"><svg width="28" height="30" viewBox="0 0 1792 1792" xmlns="http://www.w3.org/2000/svg"><path d="M63 1536h-63v-1408h63v1408zm63-1h-32v-1407h32v1407zm94 0h-31v-1407h31v1407zm157 0h-31v-1407h31v1407zm157 0h-62v-1407h62v1407zm126 0h-31v-1407h31v1407zm63 0h-31v-1407h31v1407zm63 0h-31v-1407h31v1407zm157 0h-63v-1407h63v1407zm157 0h-63v-1407h63v1407zm126 0h-63v-1407h63v1407zm126 0h-63v-1407h63v1407zm94 0h-63v-1407h63v1407zm189 0h-94v-1407h94v1407zm63 0h-32v-1407h32v1407zm94 1h-63v-1408h63v1408z" fill="#fff"/></svg></a> <p class="under-btn">I want to know about working with data in Python.</p> </div> </div> </div><div id="mc_embed_signup"> <form action="//mattmakai.us2.list-manage.com/subscribe/post?u=b7e774f0c4f05dcebbfee183d&id=b22335388d" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate> <div id="mc_embed_signup_scroll"> <h4>Sign up here to receive a monthly email with major updates to this site, tutorials and discount codes for Python books.</h4> <div class="row"> <div class="col-md-9"> <input type="email" value="" name="EMAIL" class="email form-control" id="mce-EMAIL" placeholder="email address" required> <div style="position: absolute; left: -5000px;"><input type="text" name="b_b7e774f0c4f05dcebbfee183d_b22335388d" tabindex="-1" value=""></div> </div> <div class="col-md-3"> <div class="clear"><input type="submit" value="Subscribe" name="subscribe" id="mc-embedded-subscribe" class="btn btn-success" style="font-family: 'Helvetica Neue';"></div> </div> </div> </div> </form> </div> </div> <div class="col-md-offset-1 col-md-3" id="sidebar"> <div class="panel panel-success"> <div class="panel-body"> <a href="http://www.deploypython.com/"><img src="/img/sponsored/fsp-deployment-guide.png" alt="The Full Stack Python Guide to Deployments" width="100%"></a> <p style="font-size: .8em; margin-top: 10px;">Searching for a complete, step-by-step deployment walkthrough? 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Web APIs</a><a href="/api-integration.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>API Integration</a><a href="/api-creation.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>API Creation</a><a href="/deployment.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif;'>7. 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Testing</a><a href="/unit-testing.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>Unit Testing</a><a href="/integration-testing.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>Integration Testing</a><a href="/code-metrics.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>Code Metrics</a><a href="/debugging.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>Debugging</a><a href="/what-full-stack-means.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif;'>9. Meta</a><a href="/change-log.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>Change Log</a><a href="/future-directions.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>Future Directions</a><a href="/about-author.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",sans-serif; padding-left: 27px;'>About the Author</a> <a href="/table-of-contents.html" class="list-group-item smaller-item" style='font-family: "Helvetica Neue",san-serif;background-color:#22B24C; color: #fff;'>...or <span style="border-bottom: 1px dotted;">view the full table of contents</span>.</a> </div> </div> <div class="panel panel-success"> <div class="panel-heading"><h3 class="panel-head">Object-relational Mappers (ORMs)</h3></div> <div class="panel-body"> Major updates are tweeted via <a href="https://twitter.com/fullstackpython">@fullstackpython</a>. <hr/> Need more detailed tutorials than you see here? <a href="http://www.deploypython.com/">Learn more about The Full Stack Python Guide to Deployments book.</a> </div> </div> <div class="panel panel-success" id="mobile-toc"> <div class="panel-heading"> <h3 class="panel-head"><a href="/table-of-contents.html" style="color: #fff;">Chapters</a></h3> </div> <div class="list-group"> <a href="/introduction.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>1. Introduction</a><a href="/development-environments.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>2. Development Environments</a><a href="/python-programming-language.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>3. Core Language</a><a href="/web-development.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>4. Web Development</a><a href="/data.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>5. Data</a> <a href="/object-relational-mappers-orms.html" class="list-group-item smaller-item active" style='font-family: "Helvetica Neue",sans-serif;'>» Object-relational Mappers</a> <a href="/application-programming-interfaces.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>6. Web APIs</a><a href="/deployment.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>7. Deployment</a><a href="/testing.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>8. Testing</a><a href="/what-full-stack-means.html" class="list-group-item smaller-item " style='font-family: "Helvetica Neue",sans-serif;'>9. 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