Get Invalid signature using Python script

[virtusavivek]

I have attached the python program below. Please help up to resolve.
Thanks in advance.

import sys, os, base64, datetime, hashlib, hmac 
import requests
method = 'GET'
service = 'para'
host = '{host}'
region = 'us-east-1'
endpoint = 'https://{host}/v1/_setup/s-dev'
def sign(key, msg):
    return hmac.new(key, msg.encode('utf-8'), hashlib.sha256).digest()

def getSignatureKey(key, dateStamp, regionName, serviceName):
    kDate = sign(('AWS4' + key).encode('utf-8'), dateStamp)
    kRegion = sign(kDate, regionName)
    kService = sign(kRegion, serviceName)
    kSigning = sign(kService, 'aws4_request')
    return kSigning
access_key = 'app:{rootapp}'
secret_key = ""
if access_key is None or secret_key is None:
    print('No access key is available.')
    sys.exit()
t = datetime.datetime.utcnow()
amzdate = t.strftime('%Y%m%dT%H%M%SZ')
datestamp = t.strftime('%Y%m%d')
canonical_uri = '/' 
canonical_headers = 'host:' + host + '\n' + 'x-amz-date:' + amzdate + '\n'
signed_headers = 'host;x-amz-date'
payload_hash = hashlib.sha256(('').encode('utf-8')).hexdigest()
canonical_request = method + '\n' + canonical_uri + '\n' +  canonical_headers + '\n' + signed_headers + '\n' + payload_hash
algorithm = 'AWS4-HMAC-SHA256'
credential_scope =  datestamp + '/' + region + '/' + service + '/' + 'aws4_request'
string_to_sign = algorithm + '\n' +  amzdate + '\n' +  credential_scope + '\n' +  hashlib.sha256(canonical_request.encode('utf-8')).hexdigest()
signing_key = getSignatureKey(secret_key, datestamp, region, service)
signature = hmac.new(signing_key, (string_to_sign).encode('utf-8'), hashlib.sha256).hexdigest()
authorization_header = algorithm + ' ' + 'Credential=' + access_key + '/' + credential_scope + ', ' +  'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + signature
headers = {'x-amz-date':amzdate, 'Authorization':authorization_header}

request_url = endpoint

print('\nBEGIN REQUEST++++++++++++++++++++++++++++++++++++')
print('Request URL = ' + request_url)
r = requests.get(request_url, headers=headers)

print('\nRESPONSE++++++++++++++++++++++++++++++++++++')
print('Response Headers:',headers)
print('Response code: %d\n' % r.status_code)
print(r.text)

[albogdano]

Why aren't you using the Para client for Python? There is a method there invokeSignedRequest() for that purpose.
If you are stuck, just generate a new JWT super token to access the API, using your app's secret key, as described in the Para docs.