mirror of https://github.com/pallets/flask.git
68 lines
3.5 KiB
ReStructuredText
68 lines
3.5 KiB
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Foreword for Experienced Programmers
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====================================
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This chapter is for programmers who have worked with other frameworks in the
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past, and who may have more specific or esoteric concerns that the typical
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user.
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Threads in Flask
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----------------
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One of the design decisions with Flask was that simple tasks should be simple;
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they should not take a lot of code and yet they should not limit you. Because
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of that we made a few design choices that some people might find surprising or
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unorthodox. For example, Flask uses thread-local objects internally so that
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you don’t have to pass objects around from function to function within a
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request in order to stay threadsafe. While this is a really easy approach and
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saves you a lot of time, it might also cause some troubles for very large
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applications because changes on these thread-local objects can happen anywhere
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in the same thread. In order to solve these problems we don’t hide the thread
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locals for you but instead embrace them and provide you with a lot of tools to
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make it as pleasant as possible to work with them.
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Web Development is Dangerous
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----------------------------
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If you write a web application, you are probably allowing users to register
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and leave their data on your server. The users are entrusting you with data.
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And even if you are the only user that might leave data in your application,
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you still want that data to be stored securely.
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Unfortunately, there are many ways the security of a web application can be
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compromised. Flask protects you against one of the most common security
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problems of modern web applications: cross-site scripting (XSS). Unless
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you deliberately mark insecure HTML as secure, Flask and the underlying
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Jinja2 template engine have you covered. But there are many more ways to
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cause security problems.
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The documentation will warn you about aspects of web development that
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require attention to security. Some of these security concerns
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are far more complex than one might think, and we all sometimes underestimate
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the likelihood that a vulnerability will be exploited - until a clever
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attacker figures out a way to exploit our applications. And don't think
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that your application is not important enough to attract an attacker.
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Depending on the kind of attack, chances are that automated bots are
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probing for ways to fill your database with spam, links to malicious
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software, and the like.
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So always keep security in mind when doing web development.
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The Status of Python 3
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----------------------
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Currently the Python community is in the process of improving libraries to
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support the new iteration of the Python programming language. While the
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situation is greatly improving there are still some issues that make it
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hard for us to switch over to Python 3 just now. These problems are
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partially caused by changes in the language that went unreviewed for too
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long, partially also because we have not quite worked out how the lower-
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level API should change to account for the Unicode differences in Python 3.
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Werkzeug and Flask will be ported to Python 3 as soon as a solution for
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the changes is found, and we will provide helpful tips how to upgrade
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existing applications to Python 3. Until then, we strongly recommend
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using Python 2.6 and 2.7 with activated Python 3 warnings during
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development. If you plan on upgrading to Python 3 in the near future we
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strongly recommend that you read `How to write forwards compatible
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Python code <http://lucumr.pocoo.org/2011/1/22/forwards-compatible-python/>`_.
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