The boto3 documentation states that when getting an S3 object in Python's boto3, the error S3.Client.exceptions.NoSuchKey occurs if the object does not exist. However, I didn't know how to catch this error in Python, so I tried it and investigated it.

For some reason, the behavior of get_object and head_object was different.

get_object

I was able to catch the error with the following two patterns of code.

import boto3

s3_bucket = "..."
s3_key = "..."

session = boto3.session.Session()
s3_client = session.client("s3")

try:
    s3_client.get_object(
        Bucket = s3_bucket,
        Key = s3_key,
    )
except s3_client.exceptions.NoSuchKey as e:
    "NOT FOUND ERROR!"

import boto3
import botocore.exceptions

s3_bucket = "..."
s3_key = "..."

session = boto3.session.Session()
s3_client = session.client("s3")

try:
    s3_client.get_object(
        Bucket = s3_bucket,
        Key = s3_key,
    )
except botocore.exceptions.ClientError as e:
    if e.response["Error"]["Code"] == "NoSuchKey":
        "NOT FOUND ERROR!"
    else:
        raise

The last raise is just in case there may be an error other than NoSuchKey.

head_object

I was able to catch the error with the following code.

I couldn't even try s3_client.exceptions.NoSuchKey by imitating get_object.

The catch with ClientError is also different from get_object for some reason because the string of Code is.

import boto3
import botocore.exceptions

s3_bucket = "..."
s3_key = "..."

session = boto3.session.Session()
s3_client = session.client("s3")

try:
    s3_client.head_object(
        Bucket = s3_bucket,
        Key = s3_key,
    )
except botocore.exceptions.ClientError as e:
    if e.response["Error"]["Code"] == "404":
        "NOT FOUND ERROR!"
    else:
        raise

version information

$ pip list | grep boto 
boto3                   1.14.63
botocore                1.17.63

How to catch boto3 S3 NoSuchKey error

version information