源代码: Lib/cgi.py
通用网关接口支持(CGI) 脚本的支持模块。
该模块定义了许多用Python编写的供CGI脚本使用的实用程序。
CGI脚本由HTTP服务器调用， 通常用于处理由 HTML <FORM> 元素或 <ISINDEX> 元素提交的用户输入。
通常，CGI脚本存在于服务器的特殊cgi-bin目录中。HTTP服务器将所有关于请求的信息（如客户端的主机名，请求的URL，查询字符串，以及许多其他变量）放在脚本的shell环境中，执行脚本，并将脚本的输出返回给客户。
脚本的输入也连接到客户端，有时候表单数据以这种方式读取；在其他时候，表单数据通过URL中的“查询字符串”部分传递。该模块旨在处理不同的情况，并为Python脚本提供一个更简单的接口。它还提供了许多帮助调试脚本的实用程序，最新的功能是支持表单（如果您的浏览器支持）上传文件。
CGI脚本的输出应由两个部分组成，以空行分隔。第一部分包含多个头部，它告诉客户端接下来是什么类型的数据。生成一个最小头部部分的Python代码如下所示：
print "Content-Type: text/html" # HTML is following
print # blank line, end of headers
第二部分通常是 HTML，它允许客户端软件很好地以标题、内嵌图像等方式显示格式化的文本。以下是打印一个简单HTML页面的Python代码：
print "<TITLE>CGI script output</TITLE>"
print "<H1>This is my first CGI script</H1>"
print "Hello, world!"
以写入import cgi为开始。不要使用from cgi import *——该模块定义了各种你不希望出现在命名空间里的名称供该模块使用或者向后兼容。
编写新脚本时，请考虑添加以下行：
import cgitb
cgitb.enable()
它将激活一个特殊的异常处理程序，如果发生任何错误，将在Web浏览器中显示详细的报告。如果您不想向脚本的用户显示您的程序内容，可以将报告保存到文件中，代码如下：
import cgitb
cgitb.enable(display=0, logdir="/path/to/logdir")
在脚本开发过程中使用此功能非常有帮助。由cgitb生成的报告提供了的信息可以节省大量用来跟踪错误的时间。当你测试了你的脚本，并确定它工作正常后，你可以随时删除cgitb行。
要获取提交的表单数据，最好使用FieldStorage类。该模块中定义的其他类主要用于向后兼容。将它不带参数的实例化一次。它从标准输入或环境（取决于根据CGI标准设置的各种环境变量的值）中读取表单内容。由于它可能会消耗标准输入，所以它应该只被实例化一次。
FieldStorage实例可以像Python字典一样进行索引。它允许使用in操作符进行成员身份测试，并支持标准字典方法keys()和内置函数len()。包含空字符串的表单字段将被忽略，不会出现在字典中；为了保持这些值，在创建FieldStorage实例时，为可选的keep_blank_values关键字参数提供真值。
例如，以下代码（假定Content-Type头部和空白行已经打印）检查字段name和addr 都设置为非空字符串：
form = cgi.FieldStorage()
if "name" not in form or "addr" not in form:
print "<H1>Error</H1>"
print "Please fill in the name and addr fields."
return
print "<p>name:", form["name"].value
print "<p>addr:", form["addr"].value
...further form processing here...
Here the fields, accessed through form[key], are themselves instances of FieldStorage (or MiniFieldStorage, depending on the form encoding).The value attribute of the instance yields the string value of the field. getvalue()方法直接返回此字符串值；如果所请求的密钥不存在，它也接受可选的第二个参数作为默认返回。
如果提交的表单数据包含多个具有相同名称的字段，则由形式[key]检索的对象不是FieldStorage或MiniFieldStorage实例，但是这样的实例的列表。Similarly, in this situation, form.getvalue(key) would return a list of strings. 如果您希望这种可能性（当您的HTML表单包含多个具有相同名称的字段时），请使用getlist()方法，该方法始终返回值列表（以便您不需要特殊 - 案例单项案例）。For example, this code concatenates any number of username fields, separated by commas:
value = form.getlist("username")
usernames = ",".join(value)
如果一个字段表示上传的文件，通过值属性或getvalue()方法访问该值将以内存字符串的形式读取整个文件。This may not be what you want. 您可以通过测试filename属性或文件属性来测试上传的文件。You can then read the data at leisure from the file attribute:
fileitem = form["userfile"]
if fileitem.file:
# It's an uploaded file; count lines
linecount = 0
while 1:
line = fileitem.file.readline()
if not line: break
linecount = linecount + 1
If an error is encountered when obtaining the contents of an uploaded file (for example, when the user interrupts the form submission by clicking on a Back or Cancel button) the done attribute of the object for the field will be set to the value -1.
The file upload draft standard entertains the possibility of uploading multiple files from one field (using a recursive multipart/* encoding). 发生这种情况时，该项目将是类似字典的FieldStorage项目。This can be determined by testing its type attribute, which should be multipart/form-data (or perhaps another MIME type matching multipart/*). In this case, it can be iterated over recursively just like the top-level form object.
当以“旧”格式（作为查询字符串或类型为application / x-www-form-urlencoded的单个数据部分）提交表单时，项目实际上将是class MiniFieldStorage。In this case, the list, file, and filename attributes are always None.
A form submitted via POST that also has a query string will contain both FieldStorage and MiniFieldStorage items.
New in version 2.2.
The previous section explains how to read CGI form data using the FieldStorage class. This section describes a higher level interface which was added to this class to allow one to do it in a more readable and intuitive way. The interface doesn’t make the techniques described in previous sections obsolete — they are still useful to process file uploads efficiently, for example.
The interface consists of two simple methods. Using the methods you can process form data in a generic way, without the need to worry whether only one or more values were posted under one name.
In the previous section, you learned to write following code anytime you expected a user to post more than one value under one name:
item = form.getvalue("item")
if isinstance(item, list):
# The user is requesting more than one item.
else:
# The user is requesting only one item.This situation is common for example when a form contains a group of multiple checkboxes with the same name:
<input type="checkbox" name="item" value="1" />
<input type="checkbox" name="item" value="2" />In most situations, however, there’s only one form control with a particular name in a form and then you expect and need only one value associated with this name. So you write a script containing for example this code:
user = form.getvalue("user").upper()
The problem with the code is that you should never expect that a client will provide valid input to your scripts. For example, if a curious user appends another user=foo pair to the query string, then the script would crash, because in this situation the getvalue("user") method call returns a list instead of a string. Calling the upper() method on a list is not valid (since lists do not have a method of this name) and results in an AttributeError exception.
Therefore, the appropriate way to read form data values was to always use the code which checks whether the obtained value is a single value or a list of values. That’s annoying and leads to less readable scripts.
A more convenient approach is to use the methods getfirst() and getlist() provided by this higher level interface.
This method always returns only one value associated with form field name. The method returns only the first value in case that more values were posted under such name. Please note that the order in which the values are received may vary from browser to browser and should not be counted on. [1] If no such form field or value exists then the method returns the value specified by the optional parameter default. This parameter defaults to None if not specified.
This method always returns a list of values associated with form field name. The method returns an empty list if no such form field or value exists for name. It returns a list consisting of one item if only one such value exists.
Using these methods you can write nice compact code:
import cgi
form = cgi.FieldStorage()
user = form.getfirst("user", "").upper() # This way it's safe.
for item in form.getlist("item"):
do_something(item)
自版本2.6以来已弃用。
SvFormContentDict将单值表单内容存储为字典；它假定每个字段名称仅以形式出现一次。
FormContentDict将多个值表单内容作为字典存储（表单项是值列表）。如果您的表单包含多个具有相同名称的字段，则很有用
Other classes (FormContent, InterpFormContentDict) are present for backwards compatibility with really old applications only.
These are useful if you want more control, or if you want to employ some of the algorithms implemented in this module in other circumstances.
Parse a query in the environment or from a file (the file defaults to sys.stdin and environment defaults to os.environ). The keep_blank_values and strict_parsing parameters are passed to urlparse.parse_qs() unchanged.
This function is deprecated in this module. Use urlparse.parse_qs() instead. It is maintained here only for backward compatiblity.
This function is deprecated in this module. Use urlparse.parse_qsl() instead. It is maintained here only for backward compatiblity.
Parse input of type multipart/form-data (for file uploads). Arguments are fp for the input file and pdict for a dictionary containing other parameters in the Content-Type header.
Returns a dictionary just like urlparse.parse_qs() keys are the field names, each value is a list of values for that field. This is easy to use but not much good if you are expecting megabytes to be uploaded — in that case, use the FieldStorage class instead which is much more flexible.
Note that this does not parse nested multipart parts — use FieldStorage for that.
Parse a MIME header (such as Content-Type) into a main value and a dictionary of parameters.
Robust test CGI script, usable as main program. Writes minimal HTTP headers and formats all information provided to the script in HTML form.
Format the shell environment in HTML.
Format a form in HTML.
Format the current directory in HTML.
Print a list of useful (used by CGI) environment variables in HTML.
Convert the characters '&', '<' and '>' in string s to HTML-safe sequences. Use this if you need to display text that might contain such characters in HTML. If the optional flag quote is true, the quotation mark character (") is also translated; this helps for inclusion in an HTML attribute value delimited by double quotes, as in <a href="...">. Note that single quotes are never translated.
If the value to be quoted might include single- or double-quote characters, or both, consider using the quoteattr() function in the xml.sax.saxutils module instead.
There’s one important rule: if you invoke an external program (via the os.system() or os.popen() functions. or others with similar functionality), make very sure you don’t pass arbitrary strings received from the client to the shell. This is a well-known security hole whereby clever hackers anywhere on the Web can exploit a gullible CGI script to invoke arbitrary shell commands. Even parts of the URL or field names cannot be trusted, since the request doesn’t have to come from your form!
To be on the safe side, if you must pass a string gotten from a form to a shell command, you should make sure the string contains only alphanumeric characters, dashes, underscores, and periods.
Read the documentation for your HTTP server and check with your local system administrator to find the directory where CGI scripts should be installed; usually this is in a directory cgi-bin in the server tree.
Make sure that your script is readable and executable by “others”; the Unix file mode should be 0755 octal (use chmod 0755 filename). Make sure that the first line of the script contains #! starting in column 1 followed by the pathname of the Python interpreter, for instance:
#!/usr/local/bin/python
Make sure the Python interpreter exists and is executable by “others”.
Make sure that any files your script needs to read or write are readable or writable, respectively, by “others” — their mode should be 0644 for readable and 0666 for writable. This is because, for security reasons, the HTTP server executes your script as user “nobody”, without any special privileges. It can only read (write, execute) files that everybody can read (write, execute). The current directory at execution time is also different (it is usually the server’s cgi-bin directory) and the set of environment variables is also different from what you get when you log in. In particular, don’t count on the shell’s search path for executables (PATH) or the Python module search path (PYTHONPATH) to be set to anything interesting.
If you need to load modules from a directory which is not on Python’s default module search path, you can change the path in your script, before importing other modules. For example:
import sys
sys.path.insert(0, "/usr/home/joe/lib/python")
sys.path.insert(0, "/usr/local/lib/python")
(This way, the directory inserted last will be searched first!)
Instructions for non-Unix systems will vary; check your HTTP server’s documentation (it will usually have a section on CGI scripts).
Unfortunately, a CGI script will generally not run when you try it from the command line, and a script that works perfectly from the command line may fail mysteriously when run from the server. There’s one reason why you should still test your script from the command line: if it contains a syntax error, the Python interpreter won’t execute it at all, and the HTTP server will most likely send a cryptic error to the client.
Assuming your script has no syntax errors, yet it does not work, you have no choice but to read the next section.
First of all, check for trivial installation errors — reading the section above on installing your CGI script carefully can save you a lot of time. If you wonder whether you have understood the installation procedure correctly, try installing a copy of this module file (cgi.py) as a CGI script. When invoked as a script, the file will dump its environment and the contents of the form in HTML form. Give it the right mode etc, and send it a request. If it’s installed in the standard cgi-bin directory, it should be possible to send it a request by entering a URL into your browser of the form:
http://yourhostname/cgi-bin/cgi.py?name=Joe+Blow&addr=At+HomeIf this gives an error of type 404, the server cannot find the script – perhaps you need to install it in a different directory. If it gives another error, there’s an installation problem that you should fix before trying to go any further. If you get a nicely formatted listing of the environment and form content (in this example, the fields should be listed as “addr” with value “At Home” and “name” with value “Joe Blow”), the cgi.py script has been installed correctly. If you follow the same procedure for your own script, you should now be able to debug it.
The next step could be to call the cgi module’s test() function from your script: replace its main code with the single statement
cgi.test()
This should produce the same results as those gotten from installing the cgi.py file itself.
When an ordinary Python script raises an unhandled exception (for whatever reason: of a typo in a module name, a file that can’t be opened, etc. ), the Python interpreter prints a nice traceback and exits. While the Python interpreter will still do this when your CGI script raises an exception, most likely the traceback will end up in one of the HTTP server’s log files, or be discarded altogether.
Fortunately, once you have managed to get your script to execute some code, you can easily send tracebacks to the Web browser using the cgitb module. If you haven’t done so already, just add the lines:
import cgitb
cgitb.enable()
to the top of your script. Then try running it again; when a problem occurs, you should see a detailed report that will likely make apparent the cause of the crash.
If you suspect that there may be a problem in importing the cgitb module, you can use an even more robust approach (which only uses built-in modules):
import sys
sys.stderr = sys.stdout
print "Content-Type: text/plain"
print
...your code here...
This relies on the Python interpreter to print the traceback. The content type of the output is set to plain text, which disables all HTML processing. If your script works, the raw HTML will be displayed by your client. If it raises an exception, most likely after the first two lines have been printed, a traceback will be displayed. Because no HTML interpretation is going on, the traceback will be readable.
Footnotes
| [1] | Note that some recent versions of the HTML specification do state what order the field values should be supplied in, but knowing whether a request was received from a conforming browser, or even from a browser at all, is tedious and error-prone. |