> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Python Positional-Only Parameter
Positional-only parameters are function parameters that must be supplied strictly based on their order in the function call, explicitly prohibiting the use of keyword arguments (e.g., `name=value`) for those specific parameters. Introduced in Python 3.8 (PEP 570), they are defined in a function signature using a forward slash (`/`).
All parameters declared before the `/` are enforced as positional-only. Parameters declared after the `/` retain standard Python behavior (they can be passed by position or by keyword) unless further modified by other signature operators.
## Syntax
```python theme={"dark"}
def function_name(pos_only_1, pos_only_2, /, standard_arg):
pass
```
## Mechanics and Behavior
When a function is invoked, the Python interpreter maps the provided arguments to the signature. If an argument corresponding to a positional-only parameter is passed using keyword syntax, the interpreter raises a `TypeError`.
```python theme={"dark"}
def configure_matrix(rows, columns, /, fill_value):
return [[fill_value] * columns for _ in range(rows)]
# VALID: 'rows' and 'columns' passed by position. 'fill_value' passed by position.
configure_matrix(3, 3, 0)
# VALID: 'rows' and 'columns' passed by position. 'fill_value' passed by keyword.
configure_matrix(3, 3, fill_value=0)
# INVALID: 'rows' and 'columns' passed by keyword.
configure_matrix(rows=3, columns=3, fill_value=0)
# TypeError: configure_matrix() got some positional-only arguments passed as keyword arguments: 'rows, columns'
```
## Signature Composition
The `/` operator can be combined with the `*` operator (which enforces keyword-only parameters) to create a strictly partitioned function signature. This establishes clear boundaries for argument resolution:
```python theme={"dark"}
def strict_function(pos_only, /, standard, *, kw_only):
pass
```
1. **`pos_only`**: Must be passed by position.
2. **`/`**: Demarcates the end of positional-only parameters.
3. **`standard`**: Can be passed by position or keyword.
4. **`*`**: Demarcates the start of keyword-only parameters.
5. **`kw_only`**: Must be passed by keyword.
## Default Values
Positional-only parameters support default values. However, standard rules apply: a non-default positional-only parameter cannot follow a default positional-only parameter.
```python theme={"dark"}
# VALID
def parse_data(data, strict=True, /, encoding="utf-8"):
pass
# INVALID: Non-default argument follows default argument
def parse_data(data=None, strict, /, encoding="utf-8"):
pass
```
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