Fix linting. Fix docs on mixing types. Add docs on default types.

docs/source/reference/WorkingWithTypes.md

@@ -23,8 +23,30 @@ import pystencils as ps
 import sympy as sp
 ```
 
+## Changing the Default Data Types
+
+The pystencils code generator defines two default data types:
+ - The default *numeric type*, which is applied to all numerical computations that are not
+   otherwise explicitly typed; the default is `float64`.
+ - The default *index type*, which is used for all loop and field index calculations; the default is `int64`.
+
+These can be modified by setting the
+{any}`default_dtype <CreateKernelConfig.default_dtype>` and
+{any}`index_type <CreateKernelConfig.index_dtype>`
+options of the code generator configuration:
+
+```{code-cell} ipython3
+cfg = ps.CreateKernelConfig()
+cfg.default_dtype = "float32"
+cfg.index_dtype = "int32"
+```
+
+Modifying these will change the way types for [untyped symbols](#untyped-symbols)
+and [dynamically typed expressions](#dynamic-typing) are computed.
+
 ## Setting the Types of Fields and Symbols
 
+(untyped-symbols)=
 ### Untyped Symbols
 
 Symbols used inside a kernel are most commonly created using
@@ -65,6 +87,7 @@ str(f.dtype), str(g.dtype)
 When using `Field.create_generic` or `Field.create_fixed_size`, on the other hand,
 you can set the data type via the `dtype` keyword argument.
 
+(dynamic-typing)=
 ### Dynamically Typed Symbols and Fields
 
 Apart from explicitly setting data types,
@@ -92,9 +115,11 @@ if any type conflicts arise, it will terminate with an error.
 Still, there are cases where you want to combine subexpressions of different types;
 maybe you need to compute geometric information from loop counters or other integers,
 or you are doing mixed-precision numerical computations.
-In these cases, you might have to
- 1. Introduce explicit type casts when values move from one type context to another;
- 2. Annotate expressions with a specific data type to ensure computations are performed in that type.
+In these cases, you might have to introduce explicit type casts when values move from one type context to another.
+ 
+ <!-- 2. Annotate expressions with a specific data type to ensure computations are performed in that type. 
+  TODO: See #97 (https://i10git.cs.fau.de/pycodegen/pystencils/-/issues/97)
+ -->
 
 (type_casts)=
 ### Type Casts
@@ -116,11 +141,6 @@ and then introduce a runtime cast to the target type.
 That target type must comply with the type computed for the outer expression,
 which the cast is embedded in.
 
-(explicit_expression_types)=
-### Setting Explicit Types for Expressions
-
-
-
 ## Understanding the pystencils Type Inference System
 
 To correctly apply varying data types to pystencils kernels, it is important to understand

src/pystencils/field.py

@@ -7,7 +7,7 @@ import pickle
 import re
 from enum import Enum
 from itertools import chain
-from typing import List, Optional, Sequence, Set, Tuple, Union
+from typing import List, Optional, Sequence, Set, Tuple
 from warnings import warn
 
 import numpy as np