You can use `list_append(if_not_exists())` construction.

UpdateExpression: 

    &#39;SET my_list2 = list_append(if_not_exists(my_list2, :empty_list), :my_value)&#39;

ExpressionAttributeValues: 

    { &quot;:my_value&quot;:{&quot;L&quot;: [{&quot;S&quot;:&quot;test&quot;}]}, &quot;:empty_list&quot;:{&quot;L&quot;:[]} }

An alternative to Boris solution could be to use [set][1] instead of list datatype and use the ADD keyword, it does exactly what you want. 

With Add, the update expression becomes: `ADD setName :s`

And the expression attribute values can be like: `{&quot;:s&quot;: {&quot;SS&quot;:[&quot;First&quot;, &quot;Second&quot;]}}`

http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.ADD


  [1]: http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.NamingRulesDataTypes.html#HowItWorks.DataTypes

Media Source Extension (**MSE**) needs fragmented mp4 for playback in the browser.

What exactly is Fragmented mp4(fMP4)? How is it different from normal mp4?

I&#39;ve got two branches (and master). Branch 2 is based on Branch 1 is based on master. I&#39;ve submitted Branch 1 for review, it had some changes, I rebased some of those changes into history and merged the result into master. 

Now I need to rebase Branch 2 on top of master to prepare it for review/merge.

The problem is that Branch 2 still contains the original commits of Branch 1, which don&#39;t exist anymore, so git gets confused. I tried rebase -i to drop the original commits of Branch 1, but the commits of Branch 2 don&#39;t base on top of master-before-branch-1.

What I need to do is take branch 2, drop some commits, and rebase just the remaining commits on top of master in a single operation. But I only know how to do these two operations in two distinct steps.

How can I rebase part of my branch onto another branch, dropping all commits that are not in common ancestry, except the ones I specify (e.g. from HEAD~2 up)?

Here&#39;s the current state:
  
    master                     new branch 1
    - - - - - - - - - - - | - - - - - - - - -
        \
         \   branch 1
          \ _ _ _ _ _ _ _
                         \
                          \     branch 2
                           \ _ _ _ _ _ _ _

What I want to end up with:

    master            new branch 1    
    - - - - - - - | - - - - - - - - - -
                                       \
                                        \
                                         \
                                          \    branch 2
                                           - - - - - - - - - 

Rebase only part of a branch

I&#39;m trying to use the `update_item` functionality for DynamoDB in boto3. 

I&#39;m struggling right now to update lists for items. I would like to create a new list if the list does not exist yet and otherwise append to the existing list. 

Using an `UpdateExpression` of the form `SET my_list = list_append(my_list, :my_value)` returns an error *&quot;The provided expression refers to an attribute that does not exist in the item&quot;* if the list does not exist yet.

Any idea how I would have to modify my `UpdateExpression`?

Is it possible to combine if_not_exists and list_append in update_item

I'm trying to use the <code>update_item</code> functionality for DynamoDB in boto3.
I'm struggling right now to update lists for items. I would like to create a new list if the list does not exist yet and otherwise append to the existing list.
Using an <code>UpdateExpression</code> of the form <code>SET my_list = list_append(my_list, :my_value)</code> returns an error "The provided expression refers to an attribute that does not exist in the item" if the list does not exist yet.
Any idea how I would have to modify my <code>UpdateExpression</code>?

Is there a way at all to query on the `global secondary index` of dynamodb using `boto3`. I dont find any online tutorials or resources. 

How do we query on a secondary index of dynamodb using boto3?

I&#39;m trying to update an Item in my Dynamodb Table +Users+. I have tried many different ways but I always received the same error message: 


&gt;  The provided key element does not match the schema


The creation of an Item works, as well as a query but not the update. When I check on DynamoDB the user is well created:

    {
      &quot;email&quot;: &quot;test@email.com&quot;,
      &quot;password&quot;: &quot;123&quot;,
      &quot;registration&quot;: 1460136902241,
      &quot;verified&quot;: false
    }

**Here is the table information**:

 - **Table name**: Users
 - **Primary partition key**:	email (String)
 - **Primary sort key**: registration (Number)


**Here is the code (called from lambda):**


    exports.handler = function(event, context)
    {
        var AWS = require(&quot;aws-sdk&quot;);
    
    
        var docClient = new AWS.DynamoDB.DocumentClient();
    
        var params = {
            TableName: &quot;Users&quot;,
            Item:{
                email: &quot;test@email.com&quot;,
                password: &quot;123&quot;,
                verified: false,
                registration: (new Date()).getTime(),
            }
        };
        
        // Create the user.
        
        docClient.put(params, function(err, data)
        {
            if (err)
            {
                context.fail(&quot;Put failed...&quot;);
                return;
            }
            
            var params = {
                TableName: &quot;Users&quot;,
                Key: { email : &quot;test@email.com&quot; },
                AttributeUpdates: {
                    verified: {
                        Action: &quot;PUT&quot;,
                        Value: true
                    }
                }
            };
    
            // Update the user.
            docClient.update(params, function(err, data)
            {
                if (err)
                {
                    console.log(JSON.stringify(err));
                    context.fail(JSON.stringify(err));
                    return;
                }
                context.succeed(&quot;User successfully updated.&quot;);
            });
                
            
        });
    
    };



Do you have any idea of what could be wrong in my code? 

DynamoDB - Key element does not match the schema

I know the whole design should be based on natural aggregates (documents), however I&#39;m thinking to implement a separate table for localisations (lang, key, text) and then use keys in other tables. However, I was unable to find any example on doing this. 

Any pointers might be helpful!

How to join tables in AWS DynamoDB?

My table is around 220mb with 250k records within it. I&#39;m trying to pull all of this data into python.  I realize this needs to be a chunked batch process and looped through, but I&#39;m not sure how I can set the batches to start where the previous left off.

Is there some way to filter my scan? From what I read that filtering occurs after loading and the loading stops at 1mb so I wouldn&#39;t actually be able to scan in new objects. 

Any assistance would be appreciated.

    import boto3
    dynamodb = boto3.resource(&#39;dynamodb&#39;,
        aws_session_token = aws_session_token,
        aws_access_key_id = aws_access_key_id,
        aws_secret_access_key = aws_secret_access_key,
        region_name = region
        )

    table = dynamodb.Table(&#39;widgetsTableName&#39;)

    data = table.scan()

 







Complete scan of dynamoDb with boto3

I am new to dynamodb. I want to auto increment id value when I use `putitem` with dynamodb. 

Is possible to do that?

How to use auto increment for primary key id in dynamodb

Using boto3, I can access my AWS S3 bucket:

    s3 = boto3.resource(&#39;s3&#39;)
    bucket = s3.Bucket(&#39;my-bucket-name&#39;)

Now, the bucket contains folder `first-level`, which itself contains several sub-folders named with a timestamp, for instance `1456753904534`. 
I need to know the name of these sub-folders for another job I&#39;m doing and I wonder whether I could have boto3 retrieve those for me.

So I tried:

    objs = bucket.meta.client.list_objects(Bucket=&#39;my-bucket-name&#39;)

which gives a dictionary, whose key &#39;Contents&#39; gives me all the third-level files instead of the second-level timestamp directories, in fact I get a list containing things as 

&gt; {u&#39;ETag&#39;: &#39;&quot;etag&quot;&#39;,   u&#39;Key&#39;: first-level/1456753904534/part-00014&#39;,   u&#39;LastModified&#39;:
&gt; datetime.datetime(2016, 2, 29, 13, 52, 24, tzinfo=tzutc()),  
&gt; u&#39;Owner&#39;: {u&#39;DisplayName&#39;: &#39;owner&#39;,    u&#39;ID&#39;:
&gt; &#39;id&#39;},  
&gt; u&#39;Size&#39;: size,   u&#39;StorageClass&#39;: &#39;storageclass&#39;}

you can see that the specific files, in this case `part-00014` are retrieved, while I&#39;d like to get the name of the directory alone. 
In principle I could strip out the directory name from all the paths but it&#39;s ugly and expensive to retrieve everything at third level to get the second level!

I also tried something reported [here][1]:

    for o in bucket.objects.filter(Delimiter=&#39;/&#39;):
        print(o.key)

but I do not get the folders at the desired level.

Is there a way to solve this?

  [1]: https://github.com/boto/boto3/issues/134

Retrieving subfolders names in S3 bucket from boto3

I read the filenames in my S3 bucket by doing 

    objs = boto3.client.list_objects(Bucket=&#39;my_bucket&#39;)
        while &#39;Contents&#39; in objs.keys():
            objs_contents = objs[&#39;Contents&#39;]
            for i in range(len(objs_contents)):
                filename = objs_contents[i][&#39;Key&#39;]

Now, I need to get the actual content of the file, similarly to a `open(filename).readlines()`. What is the best way?

Read file content from S3 bucket with boto3

I&#39;m trying to mock a singluar method from the boto3 s3 client object to throw an exception. But I need all other methods for this class to work as normal.

This is so I can test a singular Exception test when and error occurs performing a [upload_part_copy][1]

**1st Attempt**

    import boto3
    from mock import patch

    with patch(&#39;botocore.client.S3.upload_part_copy&#39;, side_effect=Exception(&#39;Error Uploading&#39;)) as mock:
        client = boto3.client(&#39;s3&#39;)
        # Should return actual result
        o = client.get_object(Bucket=&#39;my-bucket&#39;, Key=&#39;my-key&#39;)
        # Should return mocked exception
        e = client.upload_part_copy()

However this gives the following error:

    ImportError: No module named S3

**2nd Attempt**

After looking at the botocore.client.py source code I found that it is doing something clever and the method `upload_part_copy` does not exist. I found that it seems to call `BaseClient._make_api_call` instead so I tried to mock that

    import boto3
    from mock import patch

    with patch(&#39;botocore.client.BaseClient._make_api_call&#39;, side_effect=Exception(&#39;Error Uploading&#39;)) as mock:
        client = boto3.client(&#39;s3&#39;)
        # Should return actual result
        o = client.get_object(Bucket=&#39;my-bucket&#39;, Key=&#39;my-key&#39;)
        # Should return mocked exception
        e = client.upload_part_copy()

This throws an exception... but on the `get_object` which I want to avoid.

Any ideas about how I can only throw the exception on the `upload_part_copy` method?

  [1]: http://boto3.readthedocs.io/en/latest/reference/services/s3.html#S3.Client.upload_part_copy

Content Type	Original Author	Original Content on Stackoverflow
Question	fabian	View Question on Stackoverflow
Solution 1 - Amazon Dynamodb	Boris Serebrov	View Answer on Stackoverflow
Solution 2 - Amazon Dynamodb	Ayush Pateria	View Answer on Stackoverflow

Is it possible to combine if_not_exists and list_append in update_item

Amazon Dynamodb Problem Overview

Amazon Dynamodb Solutions

Solution 1 - Amazon Dynamodb

Solution 2 - Amazon Dynamodb

Rebase only part of a branch

What exactly is Fragmented mp4(fMP4)? How is it different from normal mp4?

Attributions