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---
title: Introduction
next: /docs/concept
---
Thinc is a **lightweight deep learning library** that offers an elegant,
type-checked, functional-programming API for **composing models**, with support
for layers defined in other frameworks such as **PyTorch**, **TensorFlow** or
**MXNet**. You can use Thinc as an interface layer, a standalone toolkit or a
flexible way to develop new models. Previous versions of Thinc have been running
quietly in production in thousands of companies, via both
[spaCy](https://spacy.io) and [Prodigy](https://prodi.gy). We wrote the new
version to let users **compose, configure and deploy custom models** built with
their favorite framework. The end result is a library quite different in its
design, that's easy to understand, plays well with others, and is a lot of fun
to use.
---
<grid layout="feature">
<div>
<code-screenshot>
[](/docs/usage-type-checking)
</code-screenshot>
</div>
<small>
##### Type-check your model definitions
with custom types and [`mypy`](https://mypy.readthedocs.io/en/stable/) plugin
<button to="/docs/usage-type-checking">Read more</button>
</small>
```python
### {small="true"}
from thinc.api import PyTorchWrapper, TensorFlowWrapper
pt_model = PyTorchWrapper(create_pytorch_model())
tf_model = TensorFlowWrapper(create_tensorflow_model())
# You can even stitch together strange hybrids
# (not efficient, but possible)
frankenmodel = chain(add(pt_model, tf_model), Linear(128), logistic())
```
<small>
##### Wrap PyTorch, TensorFlow & MXNet models for use in your network
<button to="/docs/usage-frameworks">Read more</button>
</small>
```python
### {small="true"}
def CaptionRater(
text_encoder: Model[List[str], Floats2d],
image_encoder: Model[List[Path], Floats2d]
) -> Model[Tuple[List[str], List[Path]], Floats2d]:
return chain(
concatenate(
chain(get_item(0), text_encoder),
chain(get_item(1), image_encoder)
),
residual(Relu(nO=300, dropout=0.2, normalize=True)),
Softmax(2)
)
```
<small>
##### Concise functional-programming approach to model definition
using composition rather than inheritance
<button to="/docs/usage-models">Read more</button>
</small>
```python
### {small="true"}
apply_on = lambda layer, i: chain(getitem(i), layer)
with Model.define_operators({"^": apply_on, ">>": chain, "|": concatenate}):
model = (
(text_encoder ^ 0 | image_encoder ^ 1)
>> residual(Relu(nO=300, dropout=0.2, normalize=True)
>> Softmax(2)
)
```
<small>
##### Optional custom infix notation via operator overloading
<button to="/docs/usage-models#operators">Read more</button>
</small>
```ini
### {small="true"}
[optimizer]
@optimizers = "Adam.v1"
[optimizer.learn_rate]
@schedules = "slanted_triangular.v1"
max_rate = 0.1
num_steps = 5000
```
<small>
##### Integrated config system
to describe trees of objects and hyperparameters
<button to="/docs/usage-config">Read more</button>
</small>
<!-- TODO: add one or two more lines to example -->
```python
### {small="true"}
from thinc.api import NumpyOps, set_current_ops
def CustomOps(NumpyOps):
def some_custom_op_my_layers_needs(...):
...
set_current_ops(CustomOps())
```
<small>
##### Choice of extensible backends
<button to="/docs/api-backends">Read more</button>
</small>
```python
### {small="true"}
encode_sentence = chain(
list2ragged(), # concatenate sequences
with_array( # ignore outer sequence structure (temporarily)
concatenate(Embed(128, column=0), Embed(128, column=1)),
Mish(128, dropout=0.2, normalize=True)
),
ParametricAttention(128),
reduce_mean()
)
```
<small>
##### First-class support for variable-length sequences
multiple built-in sequence representations and your layers can use any object
<button to="/docs/usage-sequences">Read more</button>
</small>
```python
### {small="true"}
for i in range(10):
for X, Y in train_batches:
Yh, backprop = model.begin_update(X)
loss, dYh = get_loss(Yh, Y)
backprop(dYh)
model.finish_update(optimizer)
```
<small>
##### Low abstraction training loop
<button to="/docs/usage-training">Read more</button>
</small>
</grid>
---
<!-- TODO: include more examples that we want to showcase -->
<tutorials>
- intro
- transformers_tagger
- parallel_training_ray
</tutorials>
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