Search code examples
pythonshellpyramid

Key error in request.params

I am a beginner in Python and I have to create a pyramid project that accepts user input from a from, and performs a simple operation that gives back the result to the user. This is my views.py 

 from pyramid.response import Response
from pyramid.view import view_config
@view_config(route_name="home",renderer='templates/ui.pt')
def my_view(request):
    myvar=request.params['command']
    return Response(myvar)

This is my templates/ui.pt (excluding all initial html,head tags)

    <form action="my_view" method="POST"><input type="text" name="command"/>
<input type="submit" name="go" value="submit"/></form>
</html>

When I run this, I get this error Keyerror:'command'

Please help.

Solution

  • If no parameters are passed in your request (which is what would happen if you visit the page without posting to it or adding a param to the query string -- http://mypage/my_view?command=something), then the request.params MultiDict won't have a key named 'command' in it and that's where your error is coming from. You can either explicitly check if 'command' is in your request.params:

    myvar = None
if 'command' in request.params:
    myvar = request.params['command']

    Or you can (more commonly) use the get method of a dictionary to supply a default value:

    myvar = request.params.get('command', None)

    Also since you're defining a template for your view, typically, your return value would be something that provides context to that template. Your code, however, isn't actually using the template but is instead directly returning a Response. You normally wouldn't do that. You'd do something more like this:

    @view_config(route_name="home",renderer='templates/ui.pt')
def my_view(request):
    myvar=request.params.get('command',None)
    return {'myvar': myvar }

    And then in your template you'd reference the object it got passed:

    <!doctype html>
<html>
<body>
<form method="POST"><input type="text" name="command"/>
<input type="submit" name="go" value="submit"/></form>
<div tal:condition="myvar">
   You entered <tal:block tal:content="myvar"></tal:block>
</div>
</body>
</html>

    Here's a walkthrough from scratch to get the above working:

    Install pyramid:

    pip install pyramid

    Create your pyramid project:

    pcreate -t starter myproject

    Set up the environment for your project:

    cd myproject
python setup.py develop

    Replace the myproject/views.py with:

    from pyramid.view import view_config

@view_config(route_name="home",renderer='templates/ui.pt')
def my_view(request):
    myvar=request.params.get('command',None)
    return {'myvar': myvar }

    Add the myproject/templates/ui.pt file:

    <!doctype html>
<html>
<body>
<form method="POST"><input type="text" name="command"/>
<input type="submit" name="go" value="submit"/></form>
<div tal:condition="myvar">
   You entered <tal:block tal:content="myvar"></tal:block>
</div>
</body>
</html>

    Start up your app:

    pserve --reload development.ini

    Visit your pyramid site:

    http://localhost:6543