To upload a list of files with the same key value in a single request, you can create a list of tuples with the first item in each tuple as the key value and the file object as the second:

files = [('file', open('report.xls', 'rb')), ('file', open('report2.xls', 'rb'))]

How to

In the template, you need to add mulitple attribute in upload input:

<form method="POST" enctype="multipart/form-data">
    <input type="file" name="photos" multiple>
    <input type="submit" value="Submit">
</form>    

Then in view function, the uploaded files can get as a list through request.files.getlist('photos'). Loop this list and call save() method on each item (werkzeug.datastructures.FileStorage) will save them at given path:

import os

from flask import Flask, request, render_template, redirect

app = Flask(__name__)
app.config['UPLOAD_PATH'] = '/the/path/to/save'

@app.route('/upload', methods=['GET', 'POST'])
def upload():
    if request.method == 'POST' and 'photo' in request.files:
        for f in request.files.getlist('photo'):
            f.save(os.path.join(app.config['UPLOAD_PATH'], f.filename))
        return 'Upload completed.'
    return render_template('upload.html')

Furthermore, you may need to use secure_filename() to clean filename:

# ...
from werkzeug.utils import secure_filename
# ...
    for f in request.files.getlist('photo'):
        filename = secure_filename(f.filename)
        f.save(os.path.join(app.config['UPLOAD_PATH'], filename))
        # ...

You can also generate a random filename with this method.

Full demo

View:

import os

from flask import Flask, request, render_template
from werkzeug.utils import secure_filename

app = Flask(__name__)  
app.config['UPLOAD_PATH'] = '/the/path/to/save'

@main.route('/upload', methods=['GET', 'POST'])
def upload():
    form = UploadForm()
    if form.validate_on_submit() and 'photo' in request.files:
        for f in request.files.getlist('photo'):
            filename = secure_filename(f.filename)
            f.save(os.path.join(app.config['UPLOAD_PATH'], filename))
        return 'Upload completed.'
    return render_template('upload.html', form=form)

Form:

from flask_wtf import FlaskForm
from wtforms import SubmitField
from flask_wtf.file import FileField, FileAllowed, FileRequired

class UploadForm(FlaskForm):
    photo = FileField('Image', validators=[
        FileRequired(),
        FileAllowed(photos, 'Image only!')
    ])
    submit = SubmitField('Submit')

Template:

<form method="POST" enctype="multipart/form-data">
    {{ form.hidden_tag() }}
    {{ form.photo(multiple="multiple") }}
    {{ form.submit }}
</form>

More

For better upload experience, you can try Flask-Dropzone.

You can use method getlist of flask.request.files, for example:

@app.route("/upload", methods=["POST"])
def upload():
    uploaded_files = flask.request.files.getlist("file[]")
    print uploaded_files
    return ""

mata's suggestion works. You can get the list of uploaded files by calling getall() on request.files.

@route('/upload', method='POST')
def do_upload():
    uploads = request.files.getall('upload')
    for upload in uploads:
        print upload.filename
    return "Found {0} files, did nothing.".format(len(uploads))