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Google Python team authored and gpshead committed Sep 17, 2020
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Expand Up @@ -463,10 +463,6 @@ library calls.

Exceptions must follow certain conditions:

- Raise exceptions like this: `raise MyError('Error message')` or `raise
MyError()`. Do not use the two-argument form (`raise MyError, 'Error
message'`).

- Make use of built-in exception classes when it makes sense. For example,
raise a `ValueError` to indicate a programming mistake like a violated
precondition (such as if you were passed a negative number but required a
Expand Down Expand Up @@ -548,16 +544,6 @@ Exceptions must follow certain conditions:
raised in the `try` block. This is often useful for cleanup, i.e., closing a
file.

- When capturing an exception, use `as` rather than a comma. For example:


```python
try:
raise Error()
except Error as error:
pass
```

<a id="s2.5-global-variables"></a>
<a id="25-global-variables"></a>

Expand Down Expand Up @@ -1376,8 +1362,8 @@ Okay to use.
<a id="decorators"></a>
### 2.17 Function and Method Decorators
Use decorators judiciously when there is a clear advantage. Avoid
`@staticmethod` and limit use of `@classmethod`.
Use decorators judiciously when there is a clear advantage. Avoid `staticmethod`
and limit use of `classmethod`.
<a id="s2.17.1-definition"></a>
<a id="2171-definition"></a>
Expand Down Expand Up @@ -1447,10 +1433,10 @@ guaranteed to succeed in all cases.
Decorators are a special case of "top level code" - see [main](#s3.17-main) for
more discussion.
Never use `@staticmethod` unless forced to in order to integrate with an API
Never use `staticmethod` unless forced to in order to integrate with an API
defined in an existing library. Write a module level function instead.
Use `@classmethod` only when writing a named constructor or a class-specific
Use `classmethod` only when writing a named constructor or a class-specific
routine that modifies necessary global state such as a process-wide cache.
<a id="s2.18-threading"></a>
Expand Down Expand Up @@ -2188,7 +2174,7 @@ aptly described using a one-line docstring.
def fetch_smalltable_rows(table_handle: smalltable.Table,
keys: Sequence[Union[bytes, str]],
require_all_keys: bool = False,
) -> Mapping[bytes, Tuple[str]]:
) -> Mapping[bytes, Tuple[str]]:
"""Fetches rows from a Smalltable.
Retrieves rows pertaining to the given keys from the Table instance
Expand Down Expand Up @@ -2225,7 +2211,7 @@ Similarly, this variation on `Args:` with a line break is also allowed:
def fetch_smalltable_rows(table_handle: smalltable.Table,
keys: Sequence[Union[bytes, str]],
require_all_keys: bool = False,
) -> Mapping[bytes, Tuple[str]]:
) -> Mapping[bytes, Tuple[str]]:
"""Fetches rows from a Smalltable.
Retrieves rows pertaining to the given keys from the Table instance
Expand Down Expand Up @@ -2649,8 +2635,8 @@ grouped from most generic to least generic:
Within each grouping, imports should be sorted lexicographically, ignoring case,
according to each module's full package path. Code may optionally place a blank
line between import sections.
according to each module's full package path (the `path` in `from path import
...`). Code may optionally place a blank line between import sections.
```python
import collections
Expand All @@ -2664,6 +2650,7 @@ import cryptography
import tensorflow as tf
from book.genres import scifi
from myproject.backend import huxley
from myproject.backend.hgwells import time_machine
from myproject.backend.state_machine import main_loop
from otherproject.ai import body
Expand Down Expand Up @@ -2756,7 +2743,7 @@ Always use a `.py` filename extension. Never use dashes.
- single character names, except for specifically allowed cases:
- counters or iterators (e.g. `i`, `j`, `k`, `v`, et al)
- counters or iterators (e.g. `i`, `j`, `k`, `v`, et al.)
- `e` as an exception identifier in `try/except` statements.
- `f` as a file handle in `with` statements
Expand Down Expand Up @@ -2904,13 +2891,11 @@ containing `exec "$0.py" "$@"`.
<a id="main"></a>
### 3.17 Main
Even a file meant to be used as an executable should be importable and a mere
import should not have the side effect of executing the program's main
functionality. The main functionality should be in a `main()` function.
In Python, `pydoc` as well as unit tests require modules to be importable. Your
code should always check `if __name__ == '__main__'` before executing your main
program so that the main program is not executed when the module is imported.
In Python, `pydoc` as well as unit tests require modules to be importable. If a
file is meant to be used as an executable, its main functionality should be in a
`main()` function, and your code should always check `if __name__ == '__main__'`
before executing your main program, so that it is not executed when the module
is imported.
When using [absl](https://github.com/abseil/abseil-py), use `app.run`:
Expand Down Expand Up @@ -3142,7 +3127,7 @@ has to be declared! You can use `Union`, but if there is only one other type,
use `Optional`.
Use explicit `Optional` instead of implicit `Optional`. Earlier versions of PEP
484 allowed `a: Text = None` to be interpretted as `a: Optional[Text] = None`,
484 allowed `a: Text = None` to be interpreted as `a: Optional[Text] = None`,
but that is no longer the preferred behavior.
```python
Expand Down

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