How to check if file exists in Google Cloud Storage?

It's as easy as use the exists method within a blob object:

from google.cloud import storage

def blob_exists(projectname, credentials, bucket_name, filename):
   client = storage.Client(projectname, credentials=credentials)
   bucket = client.get_bucket(bucket_name)
   blob = bucket.blob(filename)
   return blob.exists()

This post is old, you can actually now check if a file exists on GCP using the blob class, but because it took me a while to find an answer, adding here for the others who are looking for a solution

from google.cloud import storage

name = 'file_i_want_to_check.txt'   
storage_client = storage.Client()
bucket_name = 'my_bucket_name'
bucket = storage_client.bucket(bucket_name)
stats = storage.Blob(bucket=bucket, name=name).exists(storage_client)

Documentation is here

Hope this helps!

Edit

As per the comment by @om-prakash, if the file is in a folder, then the name should include the path to the file:

name = "folder/path_to/file_i_want_to_check.txt"