jinja2.exceptions.UndefinedError: 'form' is undefined error in python, Flask

Question

我是 Flask 新手，现在已经编程了 3 周。

我得到一个：“jinja2.exceptions.UndefinedError: 'form' is undefined error”，我不知道如何解决它。

我的主要 app.py： 这只是相关部分

 @app.route("/form", methods=["GET", "POST"])
def forms():
    global reverse_exchange_rate, exchange_rate
    form = CurrencyForm
    if request.method == 'GET':
        return render_template("form.html")

还有我的 form.html：

{% extends "layouts/main.html" %}
{% from "formhelper.html" import render_field %}

{% block content %}

    <form method="GET" action="/form">
        <div style="text-align: center">
            <h1>Currency Exchange</h1>
            {{ form.csrf_token }}
            {{ render_field(form.currency_1) }}
            {{ render_field(form.currency_2) }}
            {{ render_field(form.exchange_rate) }}
            {{ render_field(form.submit) }}
        </div>
    </form>

{% endblock %}

我收到此错误：

File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 2464, in __call__
return self.wsgi_app(environ, start_response)
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 2450, in wsgi_app
response = self.handle_exception(e)
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 1867, in handle_exception
reraise(exc_type, exc_value, tb)
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\app.py", line 1936, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "C:\Users\sport\Documents\Flask Attempt 2\app.py", line 21, in forms
return render_template("form.html")
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\templating.py", line 140, in render_template
ctx.app,
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\flask\templating.py", line 120, in _render
rv = template.render(context)
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\jinja2\environment.py", line 1090, in render
self.environment.handle_exception()
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\jinja2\environment.py", line 832, in handle_exception
reraise(*rewrite_traceback_stack(source=source))
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\jinja2\_compat.py", line 28, in reraise
raise value.with_traceback(tb)
File "C:\Users\sport\Documents\Flask Attempt 2\templates\form.html", line 2, in top-level template code
{% from "formhelper.html" import render_field %}
File "C:\Users\sport\Documents\Flask Attempt 2\templates\layouts\main.html", line 26, in top-level template code
Open an interactive python shell in this frame{% block content %}{% endblock %}
File "C:\Users\sport\Documents\Flask Attempt 2\templates\form.html", line 9, in block "content"
{{ form.csrf_token }}
File "c:\users\sport\documents\flask attempt 2\venv\lib\site-packages\jinja2\environment.py", line 471, in getattr
return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'form' is undefined

我已经尝试删除那部分 python 代码并且一切运行顺利。但如果我把它放回去，我会得到那个错误。

我也尝试将 form.html 的名称更改为 form1.html，尽管错误仍然保持不变并且说表单未定义。我不知道我的问题是什么。

form.html在templates文件夹中，文件结构正确。

感谢任何帮助。请记住，我已经编码了大约 3 周。

Answer 1

正如您在堆栈跟踪底部看到的那样，UndefinedError 来自模板行 {{ form.csrf_token }}，其中模板需要一个名为 form 的变量，但没有将此类变量传递给它。在 Flask 中解决这个问题的方法是在 render_template 函数中显式传递模板所需的所有变量作为关键字参数，例如render_template("form.html", form=form).

更多详情请参阅the relevant section of the offficial quickstart tutorial。