From 32b10d3bc4f269ff0c253df163db72d10454d4d5 Mon Sep 17 00:00:00 2001 From: kavyasrinet Date: Wed, 22 Nov 2017 12:52:01 -0800 Subject: [PATCH] Re-writing and edits in the design doc for data reader (#5849) * Updating the writeup of RNN doc * Editing the documentation for seq_decoder, and fixing typos * Fixing the captioning on 2 level RNN * pushing after a pull * Editing and re-writing parts of Data Reader design doc --- doc/design/reader/README.md | 70 ++++++++++++++++++++----------------- 1 file changed, 37 insertions(+), 33 deletions(-) diff --git a/doc/design/reader/README.md b/doc/design/reader/README.md index 320dccec3d..2cd4b6225b 100644 --- a/doc/design/reader/README.md +++ b/doc/design/reader/README.md @@ -1,25 +1,25 @@ # Python Data Reader Design Doc -At training and testing time, PaddlePaddle programs need to read data. To ease the users' work to write data reading code, we define that +During the training and testing phases, PaddlePaddle programs need to read data. To help the users write code that performs reading input data, we define the following: -- A *reader* is a function that reads data (from file, network, random number generator, etc) and yields data items. -- A *reader creator* is a function that returns a reader function. -- A *reader decorator* is a function, which accepts one or more readers, and returns a reader. -- A *batch reader* is a function that reads data (from *reader*, file, network, random number generator, etc) and yields a batch of data items. +- A *reader*: A function that reads data (from file, network, random number generator, etc) and yields the data items. +- A *reader creator*: A function that returns a reader function. +- A *reader decorator*: A function, which takes in one or more readers, and returns a reader. +- A *batch reader*: A function that reads data (from *reader*, file, network, random number generator, etc) and yields a batch of data items. -and provide function which converts reader to batch reader, frequently used reader creators and reader decorators. +and also provide a function which can convert a reader to a batch reader, frequently used reader creators and reader decorators. ## Data Reader Interface -Indeed, *data reader* doesn't have to be a function that reads and yields data items. It can be any function with no parameter that creates a iterable (anything can be used in `for x in iterable`): +*Data reader* doesn't have to be a function that reads and yields data items. It can just be any function without any parameters that creates an iterable (anything can be used in `for x in iterable`) as follows: ``` iterable = data_reader() ``` -Element produced from the iterable should be a **single** entry of data, **not** a mini batch. That entry of data could be a single item, or a tuple of items. Item should be of [supported type](http://www.paddlepaddle.org/doc/ui/data_provider/pydataprovider2.html?highlight=dense_vector#input-types) (e.g., numpy 1d array of float32, int, list of int) +The item produced from the iterable should be a **single** entry of data and **not** a mini batch. The entry of data could be a single item or a tuple of items. Item should be of one of the [supported types](http://www.paddlepaddle.org/doc/ui/data_provider/pydataprovider2.html?highlight=dense_vector#input-types) (e.g., numpy 1d array of float32, int, list of int etc.) -An example implementation for single item data reader creator: +An example implementation for single item data reader creator is as follows: ```python def reader_creator_random_image(width, height): @@ -29,7 +29,7 @@ def reader_creator_random_image(width, height): return reader ``` -An example implementation for multiple item data reader creator: +An example implementation for multiple item data reader creator is as follows: ```python def reader_creator_random_image_and_label(width, height, label): def reader(): @@ -40,9 +40,10 @@ def reader_creator_random_image_and_label(width, height, label): ## Batch Reader Interface -*batch reader* can be any function with no parameter that creates a iterable (anything can be used in `for x in iterable`). The output of the iterable should be a batch (list) of data items. Each item inside the list must be a tuple. +*Batch reader* can be any function without any parameters that creates an iterable (anything can be used in `for x in iterable`). The output of the iterable should be a batch (list) of data items. Each item inside the list should be a tuple. + +Here are some valid outputs: -Here are valid outputs: ```python # a mini batch of three data items. Each data item consist three columns of data, each of which is 1. [(1, 1, 1), @@ -58,20 +59,22 @@ Here are valid outputs: Please note that each item inside the list must be a tuple, below is an invalid output: ```python # wrong, [1,1,1] needs to be inside a tuple: ([1,1,1],). - # Otherwise it's ambiguous whether [1,1,1] means a single column of data [1, 1, 1], - # or three column of datas, each of which is 1. + # Otherwise it is ambiguous whether [1,1,1] means a single column of data [1, 1, 1], + # or three columns of data, each of which is 1. [[1,1,1], [2,2,2], [3,3,3]] ``` -It's easy to convert from reader to batch reader: +It is easy to convert from a reader to a batch reader: + ```python mnist_train = paddle.dataset.mnist.train() mnist_train_batch_reader = paddle.batch(mnist_train, 128) ``` -Also easy to create custom batch reader: +It is also straight forward to create a custom batch reader: + ```python def custom_batch_reader(): while True: @@ -85,7 +88,8 @@ mnist_random_image_batch_reader = custom_batch_reader ## Usage -batch reader, mapping from item(s) read to data layer, batch size and number of total pass will be passed into `paddle.train`: +Following is how we can use the reader with PaddlePaddle: +The batch reader, a mapping from item(s) to data layer, the batch size and the number of total passes will be passed into `paddle.train` as follows: ```python # two data layer is created: @@ -99,13 +103,13 @@ paddle.train(batch_reader, {"image":0, "label":1}, 128, 10, ...) ## Data Reader Decorator -*Data reader decorator* takes a single or multiple data reader, returns a new data reader. It is similar to a [python decorator](https://wiki.python.org/moin/PythonDecorators), but it does not use `@` syntax. +The *Data reader decorator* takes in a single reader or multiple data readers and returns a new data reader. It is similar to a [python decorator](https://wiki.python.org/moin/PythonDecorators), but it does not use `@` in the syntax. -Since we have a strict interface for data readers (no parameter, return a single data item). Data reader can be used flexiable via data reader decorators. Following are a few examples: +Since we have a strict interface for data readers (no parameters and return a single data item), a data reader can be used in a flexible way using data reader decorators. Following are a few examples: ### Prefetch Data -Since reading data may take time and training can not proceed without data. It is generally a good idea to prefetch data. +Since reading data may take some time and training can not proceed without data, it is generally a good idea to prefetch the data. Use `paddle.reader.buffered` to prefetch data: @@ -117,9 +121,9 @@ buffered_reader = paddle.reader.buffered(paddle.dataset.mnist.train(), 100) ### Compose Multiple Data Readers -For example, we want to use a source of real images (reusing mnist dataset), and a source of random images as input for [Generative Adversarial Networks](https://arxiv.org/abs/1406.2661). +For example, if we want to use a source of real images (say reusing mnist dataset), and a source of random images as input for [Generative Adversarial Networks](https://arxiv.org/abs/1406.2661). -We can do: +We can do the following : ```python def reader_creator_random_image(width, height): @@ -139,13 +143,13 @@ false_reader = reader_creator_bool(False) reader = paddle.reader.compose(paddle.dataset.mnist.train(), data_reader_creator_random_image(20, 20), true_reader, false_reader) # Skipped 1 because paddle.dataset.mnist.train() produces two items per data entry. -# And we don't care second item at this time. +# And we don't care about the second item at this time. paddle.train(paddle.batch(reader, 128), {"true_image":0, "fake_image": 2, "true_label": 3, "false_label": 4}, ...) ``` ### Shuffle -Given shuffle buffer size `n`, `paddle.reader.shuffle` will return a data reader that buffers `n` data entries and shuffle them before a data entry is read. +Given the shuffle buffer size `n`, `paddle.reader.shuffle` returns a data reader that buffers `n` data entries and shuffles them before a data entry is read. Example: ```python @@ -154,21 +158,21 @@ reader = paddle.reader.shuffle(paddle.dataset.mnist.train(), 512) ## Q & A -### Why reader return only a single entry, but not a mini batch? +### Why does a reader return only a single entry, and not a mini batch? -Always returning a single entry make reusing existing data readers much easier (e.g., if existing reader return not a single entry but 3 entries, training code will be more complex because it need to handle cases like batch size 2). +Returning a single entry makes reusing existing data readers much easier (for example, if an existing reader returns 3 entries instead if a single entry, the training code will be more complicated because it need to handle cases like a batch size 2). -We provide function `paddle.batch` to turn (single entry) reader into batch reader. +We provide a function: `paddle.batch` to turn (a single entry) reader into a batch reader. -### Why do we need batch reader, isn't train take reader and batch_size as arguments sufficient? +### Why do we need a batch reader, isn't is sufficient to give the reader and batch_size as arguments during training ? -In most of the case, train taking reader and batch_size as arguments would be sufficent. However sometimes user want to customize order of data entries inside a mini batch. Or even change batch size dynamically. +In most of the cases, it would be sufficient to give the reader and batch_size as arguments to the train method. However sometimes the user wants to customize the order of data entries inside a mini batch, or even change the batch size dynamically. For these cases using a batch reader is very efficient and helpful. -### Why use a dictionary but not a list to provide mapping? +### Why use a dictionary instead of a list to provide mapping? -We decided to use dictionary (`{"image":0, "label":1}`) instead of list (`["image", "label"]`) is because that user can easily resue item (e.g., using `{"image_a":0, "image_b":0, "label":1}`) or skip item (e.g., using `{"image_a":0, "label":2}`). +Using a dictionary (`{"image":0, "label":1}`) instead of a list (`["image", "label"]`) gives the advantage that the user can easily reuse the items (e.g., using `{"image_a":0, "image_b":0, "label":1}`) or even skip an item (e.g., using `{"image_a":0, "label":2}`). -### How to create custom data reader creator +### How to create a custom data reader creator ? ```python def image_reader_creator(image_path, label_path, n): @@ -192,7 +196,7 @@ paddle.train(paddle.batch(reader, 128), {"image":0, "label":1}, ...) ### How is `paddle.train` implemented -An example implementation of paddle.train could be: +An example implementation of paddle.train is: ```python def train(batch_reader, mapping, batch_size, total_pass): -- GitLab