Python Requests - URL changes between params as text vs params as dictionary - python-2.7

Question

I'm using Python Requests to call an API using GET
I generate a signature using hmac and hashlib which results in a signature that looks like:
4epwTDKhWcIJL6bMM5f2hmBrOoXXIGD9UwX8ErfYzqU%3D
When I use Requests and specify the params as a string, the API call is successful because the signature is used as-is and doesn't change.
However when I use Requests and specify the params as a dictionary, the signature above is somehow URL encoded again, resulting in the % being encoded to %25, causing the signature to display as follows (note the %25):
4epwTDKhWcIJL6bMM5f2hmBrOoXXIGD9UwX8ErfYzqU%253D
For more context, here is the string params:
url = 'https://example.com/API'
payload = '&parameterA=valueA&parameterB=valueB&parameterC=valueC& apikey='+apikey+'&salt='+salt+'&signature='+sig
#payload = {'parameterA': 'valueA', 'parameterB': 'valueB', 'apikey': apikey, 'salt': salt, 'signature': sig}
r = requests.get(url, params=payload)
print r.url
results in a URL of:
https://example.com/API&
&parameterA=valueA
&parameterB=valueB
&apikey=0e1026af-40ce-e354-f1f2-72d280ca122
&salt=12345
&signature=4epwTDKhWcIJL6bMM5f2hmBrOoXXIGD9UwX8ErfYzqU%3D
Now, the dictionary params:
url = 'https://example.com/API'
payload = {'parameterA': 'valueA', 'parameterB': 'valueB', 'apikey': apikey, 'salt': salt, 'signature': sig}
r = requests.get(url, params=payload)
print r.url
results in a URL of:
https://example.com/API
&signature=4epwTDKhWcIJL6bMM5f2hmBrOoXXIGD9UwX8ErfYzqU%253D
&salt=12345
&apikey=0e1026af-40ce-e354-f1f2-72d280ca122
&parameterA=valueA
&parameterB=valueB
Note again that the % in the signature has changed to %25
Thanks!

Answer 1

When passing a dictionary to params it gets url encoded. Your string is url encoded already so it gets double encoded, resulting in a malformed 'signature'.
You can use urllib.unquote to decode sig (or you can just replace '%3D' with '=')
payload = {
'parameterA': 'valueA', 'parameterB': 'valueB',
'apikey': apikey, 'salt': salt, 'signature': urllib.unquote(sig)
}
Note that in python3 unquote is located in urllib.parse.