Merge pull request #1062 from SteelyWing/patch-2

Doc for add check upload file

docs/patterns/fileuploads.rst

@@ -56,7 +56,16 @@ the file and redirects the user to the URL for the uploaded file::
     @app.route('/', methods=['GET', 'POST'])
     def upload_file():
         if request.method == 'POST':
+            # check if the post request has the file part
+            if 'file' not in request.files:
+                flash('No file part')
+                return redirect(request.url)
             file = request.files['file']
+            # if user does not select file, browser also
+            # submit a empty part without filename
+            if file.filename == '':
+                flash('No selected file')
+                return redirect(request.url)
             if file and allowed_file(file.filename):
                 filename = secure_filename(file.filename)
                 file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))