Lambda error: Could not unzip uploaded file

I’m trying to update lambda function code

import base64
import boto3
import glob
import os
import zipfile
from StringIO import StringIO

buf = StringIO()
with zipfile.ZipFile(buf, 'w') as z:
    for f in glob.glob(os.path.join(os.path.dirname(__file__), 'app/*.py')):
        z.write(os.path.abspath(f), os.path.basename(f))
buf.seek(0)
pkg = base64.b64encode(buf.read())

client = boto3.client('lambda')
res = client.update_function_code(
    FunctionName='my_function',
    ZipFile=pkg,
    Publish=False
)

Get the ClientError

botocore.exceptions.ClientError: An error occurred (InvalidParameterValueException) when calling the UpdateFunctionCode operation: Could not unzip uploaded file. Please check your file, then try to upload again.

I tried to upload the same package with awscli and it works fine

aws lambda update-function-code --function-name my_function --zip-file=fileb://app.zip

My environment

Python 2.7.9
boto3==1.2.3
botocore==1.3.25

[jingpengw]

in case this is useful for anyone, this works.

 buf = StringIO()                     
 with zipfile.ZipFile(buf, 'w') as z: 
     z.write(script_name)             
 buf.seek(0)                          
 return buf.read()                    

[michaeleliot]

I resolved the issue by following this guide. My final code was:

with open('my-deployment-package.zip', 'rb') as f:
	zipped_code = f.read()

client.create_function(
  FunctionName = "FUNCTION_NAME",
  Runtime = "python3.6",
  Code=dict(ZipFile=zipped_code),
  Handler = "FILE.FUNCTION",
  Role = "ROLE"
)