AppleScript Dialog gives error? My AppleScript app on my computer gives a error.

Here is the code:

set file to display dialog "Open Script?" default answer "tests/helloworld.in"
do shell script "cat " &amp; file &amp; " | python parenthetic.py"
do shell script "echo"
do shell script "echo App +" &amp; file  &amp; "+ is done load!"


And the error:


  Can't set file to display dialog "Open Script?" default answer "tests/helloworld.in". Access not allowed.
You can't set file because it's reserved by AppleScript.

Rename file to something else, such as myfile.