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I have a flask app which communicates with another web service. I have this error which only seems to occur when both applications are running on the same server, but I don't know what the source is. The Flask application is hosted at /tools via a WSGIScriptAlias in Apache.
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] mod_wsgi (pid=25705): Exception occurred processing WSGI script '/opt/tools-frontend/wsgi.py'.
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] Traceback (most recent call last):
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] return self.wsgi_app(environ, start_response)
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/flask/app.py", line 1689, in wsgi_app
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] response = self.make_response(self.handle_exception(e))
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/flask/app.py", line 1687, in wsgi_app
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] response = self.full_dispatch_request()
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/flask/app.py", line 1361, in full_dispatch_request
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] response = self.make_response(rv)
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/flask/app.py", line 1447, in make_response
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] rv = self.response_class(rv, headers=headers, status=status)
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/werkzeug/wrappers.py", line 627, in __init__
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] self.headers = Headers(headers)
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/werkzeug/datastructures.py", line 836, in __init__
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] self.extend(defaults)
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] File "/opt/tools-frontend/ENV_1/lib/python2.7/site-packages/werkzeug/datastructures.py", line 978, in extend
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] for key, value in iterable:
[Thu May 23 13:11:44 2013] [error] [client 41.164.8.114] ValueError: too many values to unpack
[Thu May 23 13:11:44 2013] [debug] mod_deflate.c(615): [client 41.164.8.114] Zlib: Compressed 590 to 372 : URL /tools/api/login/, referer: http://www.website.com/tools
The API is hosted at a different domain on the same machine, looking at the log file for that, it is working correctly.
The API call is made in the following functions:
@app.route('/api/', methods=['GET', 'POST', 'PUT', 'DELETE'])
@app.route('/api/<path:endpoint>', methods=['GET', 'POST', 'PUT', 'DELETE'])
def api(endpoint=None):
# extract POST/PUT variables
dat = request.form
if len(dat) == 0:
# extract GET variables
dat = request.args
# submit request to API
out = call_api(request.method, endpoint, dat, request.files)
return out
which calls:
def call_api(method, endpoint, data=None, files=None):
url = 'https://api.example.com' + endpoint
if method.upper() == "GET":
r = requests.get(url, data=data, verify=False)
# ... similarly for other verbs
return r.text, r.status_code, r.headers
805
The Python "ValueError: too many values to unpack (expected 2) in Python" occurs when the number of variables in the assignment is not the same as the number of values in the iterable. To solve the error, declare exactly as many variables as there are items in the iterable.
To solve this problem, use the items() method to iterate over a dictionary. Another common cause is when you try to unpack too many values into variables without assigning enough variables. You solve this issue by ensuring the number of variables to which a list unpacked is equal to the number of items in the list.
The valueerror: too many values to unpack occurs during a multiple-assignment where you either don't have enough objects to assign to the variables or you have more objects to assign than variables.
My best guess is that you return a special headers dictionary (from python-requests) instead of a normal one. Flask takes the headers in two forms:
{'key': 'value'}
# and
[('key', 'value')]
Since your special dict is not recognized as a real dict, it will be treated like a list of tuples, which fails.
Change
return r.text, r.status_code, r.headers
to
return r.text, r.status_code, r.headers.items()
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