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446 lines
17 KiB
Plaintext
============
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File Uploads
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============
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.. currentmodule:: django.core.files.uploadedfile
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When Django handles a file upload, the file data ends up placed in
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:attr:`request.FILES <django.http.HttpRequest.FILES>` (for more on the
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``request`` object see the documentation for :doc:`request and response objects
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</ref/request-response>`). This document explains how files are stored on disk
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and in memory, and how to customize the default behavior.
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Basic file uploads
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==================
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Consider a simple form containing a :class:`~django.forms.FileField`::
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from django import forms
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class UploadFileForm(forms.Form):
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title = forms.CharField(max_length=50)
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file = forms.FileField()
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A view handling this form will receive the file data in
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:attr:`request.FILES <django.http.HttpRequest.FILES>`, which is a dictionary
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containing a key for each :class:`~django.forms.FileField` (or
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:class:`~django.forms.ImageField`, or other :class:`~django.forms.FileField`
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subclass) in the form. So the data from the above form would
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be accessible as ``request.FILES['file']``.
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Note that :attr:`request.FILES <django.http.HttpRequest.FILES>` will only
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contain data if the request method was ``POST`` and the ``<form>`` that posted
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the request has the attribute ``enctype="multipart/form-data"``. Otherwise,
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``request.FILES`` will be empty.
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Most of the time, you'll simply pass the file data from ``request`` into the
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form as described in :ref:`binding-uploaded-files`. This would look
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something like::
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from django.http import HttpResponseRedirect
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from django.shortcuts import render_to_response
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# Imaginary function to handle an uploaded file.
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from somewhere import handle_uploaded_file
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def upload_file(request):
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if request.method == 'POST':
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form = UploadFileForm(request.POST, request.FILES)
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if form.is_valid():
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handle_uploaded_file(request.FILES['file'])
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return HttpResponseRedirect('/success/url/')
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else:
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form = UploadFileForm()
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return render_to_response('upload.html', {'form': form})
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Notice that we have to pass :attr:`request.FILES <django.http.HttpRequest.FILES>`
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into the form's constructor; this is how file data gets bound into a form.
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Handling uploaded files
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-----------------------
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.. class:: UploadedFile
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The final piece of the puzzle is handling the actual file data from
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:attr:`request.FILES <django.http.HttpRequest.FILES>`. Each entry in this
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dictionary is an ``UploadedFile`` object -- a simple wrapper around an uploaded
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file. You'll usually use one of these methods to access the uploaded content:
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.. method:: read()
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Read the entire uploaded data from the file. Be careful with this
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method: if the uploaded file is huge it can overwhelm your system if you
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try to read it into memory. You'll probably want to use ``chunks()``
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instead; see below.
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.. method:: multiple_chunks()
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Returns ``True`` if the uploaded file is big enough to require
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reading in multiple chunks. By default this will be any file
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larger than 2.5 megabytes, but that's configurable; see below.
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.. method:: chunks()
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A generator returning chunks of the file. If ``multiple_chunks()`` is
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``True``, you should use this method in a loop instead of ``read()``.
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In practice, it's often easiest simply to use ``chunks()`` all the time;
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see the example below.
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.. attribute:: name
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The name of the uploaded file (e.g. ``my_file.txt``).
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.. attribute:: size
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The size, in bytes, of the uploaded file.
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There are a few other methods and attributes available on ``UploadedFile``
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objects; see `UploadedFile objects`_ for a complete reference.
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Putting it all together, here's a common way you might handle an uploaded file::
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def handle_uploaded_file(f):
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with open('some/file/name.txt', 'wb+') as destination:
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for chunk in f.chunks():
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destination.write(chunk)
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Looping over ``UploadedFile.chunks()`` instead of using ``read()`` ensures that
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large files don't overwhelm your system's memory.
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Where uploaded data is stored
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-----------------------------
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Before you save uploaded files, the data needs to be stored somewhere.
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By default, if an uploaded file is smaller than 2.5 megabytes, Django will hold
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the entire contents of the upload in memory. This means that saving the file
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involves only a read from memory and a write to disk and thus is very fast.
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However, if an uploaded file is too large, Django will write the uploaded file
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to a temporary file stored in your system's temporary directory. On a Unix-like
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platform this means you can expect Django to generate a file called something
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like ``/tmp/tmpzfp6I6.upload``. If an upload is large enough, you can watch this
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file grow in size as Django streams the data onto disk.
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These specifics -- 2.5 megabytes; ``/tmp``; etc. -- are simply "reasonable
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defaults". Read on for details on how you can customize or completely replace
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upload behavior.
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Changing upload handler behavior
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--------------------------------
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Three settings control Django's file upload behavior:
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:setting:`FILE_UPLOAD_MAX_MEMORY_SIZE`
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The maximum size, in bytes, for files that will be uploaded into memory.
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Files larger than :setting:`FILE_UPLOAD_MAX_MEMORY_SIZE` will be
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streamed to disk.
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Defaults to 2.5 megabytes.
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:setting:`FILE_UPLOAD_TEMP_DIR`
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The directory where uploaded files larger than
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:setting:`FILE_UPLOAD_MAX_MEMORY_SIZE` will be stored.
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Defaults to your system's standard temporary directory (i.e. ``/tmp`` on
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most Unix-like systems).
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:setting:`FILE_UPLOAD_PERMISSIONS`
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The numeric mode (i.e. ``0644``) to set newly uploaded files to. For
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more information about what these modes mean, see the documentation for
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:func:`os.chmod`.
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If this isn't given or is ``None``, you'll get operating-system
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dependent behavior. On most platforms, temporary files will have a mode
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of ``0600``, and files saved from memory will be saved using the
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system's standard umask.
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.. warning::
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If you're not familiar with file modes, please note that the leading
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``0`` is very important: it indicates an octal number, which is the
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way that modes must be specified. If you try to use ``644``, you'll
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get totally incorrect behavior.
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**Always prefix the mode with a 0.**
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:setting:`FILE_UPLOAD_HANDLERS`
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The actual handlers for uploaded files. Changing this setting allows
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complete customization -- even replacement -- of Django's upload
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process. See `upload handlers`_, below, for details.
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Defaults to::
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("django.core.files.uploadhandler.MemoryFileUploadHandler",
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"django.core.files.uploadhandler.TemporaryFileUploadHandler",)
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Which means "try to upload to memory first, then fall back to temporary
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files."
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Handling uploaded files with a model
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------------------------------------
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If you're saving a file on a :class:`~django.db.models.Model` with a
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:class:`~django.db.models.FileField`, using a :class:`~django.forms.ModelForm`
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makes this process much easier. The file object will be saved to the location
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specified by the :attr:`~django.db.models.FileField.upload_to` argument of the
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corresponding :class:`~django.db.models.FileField` when calling
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``form.save()``::
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from django.http import HttpResponseRedirect
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from django.shortcuts import render
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from .forms import ModelFormWithFileField
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def upload_file(request):
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if request.method == 'POST':
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form = ModelFormWithFileField(request.POST, request.FILES)
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if form.is_valid():
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# file is saved
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form.save()
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return HttpResponseRedirect('/success/url/')
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else:
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form = ModelFormWithFileField()
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return render('upload.html', {'form': form})
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If you are constructing an object manually, you can simply assign the file
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object from :attr:`request.FILES <django.http.HttpRequest.FILES>` to the file
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field in the model::
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from django.http import HttpResponseRedirect
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from django.shortcuts import render
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from .forms import UploadFileForm
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from .models import ModelWithFileField
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def upload_file(request):
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if request.method == 'POST':
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form = UploadFileForm(request.POST, request.FILES)
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if form.is_valid():
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instance = ModelWithFileField(file_field=request.FILES['file'])
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instance.save()
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return HttpResponseRedirect('/success/url/')
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else:
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form = UploadFileForm()
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return render('upload.html', {'form': form})
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``UploadedFile`` objects
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========================
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In addition to those inherited from :class:`File`, all ``UploadedFile`` objects
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define the following methods/attributes:
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.. attribute:: UploadedFile.content_type
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The content-type header uploaded with the file (e.g. :mimetype:`text/plain`
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or :mimetype:`application/pdf`). Like any data supplied by the user, you
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shouldn't trust that the uploaded file is actually this type. You'll still
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need to validate that the file contains the content that the content-type
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header claims -- "trust but verify."
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.. attribute:: UploadedFile.charset
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For :mimetype:`text/*` content-types, the character set (i.e. ``utf8``)
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supplied by the browser. Again, "trust but verify" is the best policy here.
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.. attribute:: UploadedFile.temporary_file_path()
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Only files uploaded onto disk will have this method; it returns the full
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path to the temporary uploaded file.
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.. note::
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Like regular Python files, you can read the file line-by-line simply by
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iterating over the uploaded file:
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.. code-block:: python
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for line in uploadedfile:
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do_something_with(line)
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However, *unlike* standard Python files, :class:`UploadedFile` only
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understands ``\n`` (also known as "Unix-style") line endings. If you know
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that you need to handle uploaded files with different line endings, you'll
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need to do so in your view.
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Upload Handlers
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===============
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When a user uploads a file, Django passes off the file data to an *upload
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handler* -- a small class that handles file data as it gets uploaded. Upload
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handlers are initially defined in the :setting:`FILE_UPLOAD_HANDLERS` setting,
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which defaults to::
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("django.core.files.uploadhandler.MemoryFileUploadHandler",
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"django.core.files.uploadhandler.TemporaryFileUploadHandler",)
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Together the ``MemoryFileUploadHandler`` and ``TemporaryFileUploadHandler``
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provide Django's default file upload behavior of reading small files into memory
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and large ones onto disk.
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You can write custom handlers that customize how Django handles files. You
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could, for example, use custom handlers to enforce user-level quotas, compress
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data on the fly, render progress bars, and even send data to another storage
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location directly without storing it locally.
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.. _modifying_upload_handlers_on_the_fly:
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Modifying upload handlers on the fly
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------------------------------------
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Sometimes particular views require different upload behavior. In these cases,
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you can override upload handlers on a per-request basis by modifying
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``request.upload_handlers``. By default, this list will contain the upload
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handlers given by :setting:`FILE_UPLOAD_HANDLERS`, but you can modify the list
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as you would any other list.
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For instance, suppose you've written a ``ProgressBarUploadHandler`` that
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provides feedback on upload progress to some sort of AJAX widget. You'd add this
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handler to your upload handlers like this::
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request.upload_handlers.insert(0, ProgressBarUploadHandler())
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You'd probably want to use ``list.insert()`` in this case (instead of
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``append()``) because a progress bar handler would need to run *before* any
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other handlers. Remember, the upload handlers are processed in order.
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If you want to replace the upload handlers completely, you can just assign a new
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list::
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request.upload_handlers = [ProgressBarUploadHandler()]
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.. note::
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You can only modify upload handlers *before* accessing
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``request.POST`` or ``request.FILES`` -- it doesn't make sense to
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change upload handlers after upload handling has already
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started. If you try to modify ``request.upload_handlers`` after
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reading from ``request.POST`` or ``request.FILES`` Django will
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throw an error.
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Thus, you should always modify uploading handlers as early in your view as
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possible.
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Also, ``request.POST`` is accessed by
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:class:`~django.middleware.csrf.CsrfViewMiddleware` which is enabled by
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default. This means you will need to use
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:func:`~django.views.decorators.csrf.csrf_exempt` on your view to allow you
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to change the upload handlers. You will then need to use
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:func:`~django.views.decorators.csrf.csrf_protect` on the function that
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actually processes the request. Note that this means that the handlers may
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start receiving the file upload before the CSRF checks have been done.
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Example code:
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.. code-block:: python
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from django.views.decorators.csrf import csrf_exempt, csrf_protect
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@csrf_exempt
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def upload_file_view(request):
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request.upload_handlers.insert(0, ProgressBarUploadHandler())
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return _upload_file_view(request)
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@csrf_protect
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def _upload_file_view(request):
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... # Process request
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Writing custom upload handlers
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------------------------------
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All file upload handlers should be subclasses of
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``django.core.files.uploadhandler.FileUploadHandler``. You can define upload
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handlers wherever you wish.
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Required methods
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~~~~~~~~~~~~~~~~
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Custom file upload handlers **must** define the following methods:
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``FileUploadHandler.receive_data_chunk(self, raw_data, start)``
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Receives a "chunk" of data from the file upload.
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``raw_data`` is a byte string containing the uploaded data.
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``start`` is the position in the file where this ``raw_data`` chunk
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begins.
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The data you return will get fed into the subsequent upload handlers'
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``receive_data_chunk`` methods. In this way, one handler can be a
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"filter" for other handlers.
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Return ``None`` from ``receive_data_chunk`` to sort-circuit remaining
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upload handlers from getting this chunk.. This is useful if you're
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storing the uploaded data yourself and don't want future handlers to
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store a copy of the data.
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If you raise a ``StopUpload`` or a ``SkipFile`` exception, the upload
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will abort or the file will be completely skipped.
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``FileUploadHandler.file_complete(self, file_size)``
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Called when a file has finished uploading.
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The handler should return an ``UploadedFile`` object that will be stored
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in ``request.FILES``. Handlers may also return ``None`` to indicate that
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the ``UploadedFile`` object should come from subsequent upload handlers.
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Optional methods
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~~~~~~~~~~~~~~~~
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Custom upload handlers may also define any of the following optional methods or
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attributes:
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``FileUploadHandler.chunk_size``
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Size, in bytes, of the "chunks" Django should store into memory and feed
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into the handler. That is, this attribute controls the size of chunks
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fed into ``FileUploadHandler.receive_data_chunk``.
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For maximum performance the chunk sizes should be divisible by ``4`` and
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should not exceed 2 GB (2\ :sup:`31` bytes) in size. When there are
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multiple chunk sizes provided by multiple handlers, Django will use the
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smallest chunk size defined by any handler.
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The default is 64*2\ :sup:`10` bytes, or 64 KB.
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``FileUploadHandler.new_file(self, field_name, file_name, content_type, content_length, charset)``
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Callback signaling that a new file upload is starting. This is called
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before any data has been fed to any upload handlers.
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``field_name`` is a string name of the file ``<input>`` field.
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``file_name`` is the unicode filename that was provided by the browser.
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``content_type`` is the MIME type provided by the browser -- E.g.
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``'image/jpeg'``.
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``content_length`` is the length of the image given by the browser.
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Sometimes this won't be provided and will be ``None``.
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``charset`` is the character set (i.e. ``utf8``) given by the browser.
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Like ``content_length``, this sometimes won't be provided.
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This method may raise a ``StopFutureHandlers`` exception to prevent
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future handlers from handling this file.
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``FileUploadHandler.upload_complete(self)``
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Callback signaling that the entire upload (all files) has completed.
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``FileUploadHandler.handle_raw_input(self, input_data, META, content_length, boundary, encoding)``
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Allows the handler to completely override the parsing of the raw
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HTTP input.
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``input_data`` is a file-like object that supports ``read()``-ing.
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``META`` is the same object as ``request.META``.
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``content_length`` is the length of the data in ``input_data``. Don't
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read more than ``content_length`` bytes from ``input_data``.
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``boundary`` is the MIME boundary for this request.
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``encoding`` is the encoding of the request.
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Return ``None`` if you want upload handling to continue, or a tuple of
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``(POST, FILES)`` if you want to return the new data structures suitable
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for the request directly.
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