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@ -306,31 +306,32 @@ All new code should import each module by its full package name.
Imports should be as follows: Imports should be as follows:
```python
Yes: Yes:
# Reference absl.flags in code with the complete name (verbose).
import absl.flags
from doctor.who import jodie
```python FLAGS = absl.flags.FLAGS
# Reference absl.flags in code with the complete name (verbose).
import absl.flags
from doctor.who import jodie
FLAGS = absl.flags.FLAGS
``` ```
```python ```python
# Reference flags in code with just the module name (common). Yes:
from absl import flags # Reference flags in code with just the module name (common).
from doctor.who import jodie from absl import flags
from doctor.who import jodie
FLAGS = flags.FLAGS FLAGS = flags.FLAGS
``` ```
No: _(assume this file lives in `doctor/who/` where `jodie.py` also exists)_ _(assume this file lives in `doctor/who/` where `jodie.py` also exists)_
```python ```python
# Unclear what module the author wanted and what will be imported. The actual No:
# import behavior depends on external factors controlling sys.path. # Unclear what module the author wanted and what will be imported. The actual
# Which possible jodie module did the author intend to import? # import behavior depends on external factors controlling sys.path.
import jodie # Which possible jodie module did the author intend to import?
import jodie
``` ```
The directory the main binary is located in should not be assumed to be in The directory the main binary is located in should not be assumed to be in
@ -441,7 +442,7 @@ Exceptions must follow certain conditions:
- Libraries or packages may define their own exceptions. When doing so they - Libraries or packages may define their own exceptions. When doing so they
must inherit from an existing exception class. Exception names should end in must inherit from an existing exception class. Exception names should end in
`Error` and should not introduce stutter (`foo.FooError`). `Error` and should not introduce repetition (`foo.FooError`).
- Never use catch-all `except:` statements, or catch `Exception` or - Never use catch-all `except:` statements, or catch `Exception` or
`StandardError`, unless you are `StandardError`, unless you are
@ -968,8 +969,10 @@ No: def foo(a, b: Mapping = {}): # Could still get passed to unchecked code
<a id="properties"></a> <a id="properties"></a>
### 2.13 Properties ### 2.13 Properties
Use properties for accessing or setting data where you would normally have used Properties may be used to control getting or setting attributes that require
simple, lightweight accessor or setter methods. trivial, but unsurprising, computations or logic. Property implementations must
match the general expectations of regular attribute access: that they are cheap,
straightforward, and unsurprising.
<a id="s2.13.1-definition"></a> <a id="s2.13.1-definition"></a>
<a id="2131-definition"></a> <a id="2131-definition"></a>
@ -1008,9 +1011,19 @@ subclasses.
<a id="properties-decision"></a> <a id="properties-decision"></a>
#### 2.13.4 Decision #### 2.13.4 Decision
Use properties in new code to access or set data where you would normally have Properties are allowed, but, like operator overloading, should only be used when
used lightweight accessor or setter methods. Properties should be created with necessary and match the expectations of typical attribute access; follow the
the `@property` [decorator](#s2.17-function-and-method-decorators). [getters and setters](#getters-and-setters) rules otherwise.
For example, using a property to simply both get and set an internal attribute
isn't allowed: there is no computation occurring, so the property is unnecessary
([make it public instead](#getters-and-setters)). In comparison, using a
property to control attribute access, or calculate a *trivially* derived value,
is allowed: the logic is trivial, but unsurprising.
Properties should be created with the `@property`
[decorator](#s2.17-function-and-method-decorators). Manually implementing a
property descriptor is considered a [power feature](#power-features).
Inheritance with properties can be non-obvious if the property itself is not Inheritance with properties can be non-obvious if the property itself is not
overridden. Thus one must make sure that accessor methods are called indirectly overridden. Thus one must make sure that accessor methods are called indirectly
@ -1127,9 +1140,6 @@ Use the "implicit" false if possible, e.g., `if foo:` rather than `if foo !=
Yes: if not users: Yes: if not users:
print('no users') print('no users')
if foo == 0:
self.handle_zero()
if i % 10 == 0: if i % 10 == 0:
self.handle_multiple_of_ten() self.handle_multiple_of_ten()
@ -1142,9 +1152,6 @@ Use the "implicit" false if possible, e.g., `if foo:` rather than `if foo !=
No: if len(users) == 0: No: if len(users) == 0:
print('no users') print('no users')
if foo is not None and not foo:
self.handle_zero()
if not i % 10: if not i % 10:
self.handle_multiple_of_ten() self.handle_multiple_of_ten()
@ -1805,6 +1812,10 @@ definitions. One blank line between method definitions and between the `class`
line and the first method. No blank line following a `def` line. Use single line and the first method. No blank line following a `def` line. Use single
blank lines as you judge appropriate within functions or methods. blank lines as you judge appropriate within functions or methods.
Blank lines need not be anchored to the definition. For example, related
comments immediately preceding function, class, and method definitions can make
sense. Consider if your comment might be more useful as part of the docstring.
<a id="s3.6-whitespace"></a> <a id="s3.6-whitespace"></a>
<a id="36-whitespace"></a> <a id="36-whitespace"></a>
@ -2050,7 +2061,14 @@ aptly described using a one-line docstring.
returns None, this section is not required. It may also be omitted if the returns None, this section is not required. It may also be omitted if the
docstring starts with Returns or Yields (e.g. `"""Returns row from Bigtable docstring starts with Returns or Yields (e.g. `"""Returns row from Bigtable
as a tuple of strings."""`) and the opening sentence is sufficient to as a tuple of strings."""`) and the opening sentence is sufficient to
describe return value. describe the return value. Do not imitate 'NumPy style'
([example](http://numpy.org/doc/stable/reference/generated/numpy.linalg.qr.html)),
which frequently documents a tuple return value as if it were multiple
return values with individual names (never mentioning the tuple). Instead,
describe such a return value as: "Returns a tuple (mat_a, mat_b), where
mat_a is ..., and ...". The auxiliary names in the docstring need not
necessarily correspond to any internal names used in the function body (as
those are not part of the API).
<a id="doc-function-raises"></a> <a id="doc-function-raises"></a>
[*Raises:*](#doc-function-raises) [*Raises:*](#doc-function-raises)
@ -2075,8 +2093,8 @@ def fetch_smalltable_rows(table_handle: smalltable.Table,
table_handle: An open smalltable.Table instance. table_handle: An open smalltable.Table instance.
keys: A sequence of strings representing the key of each table keys: A sequence of strings representing the key of each table
row to fetch. String keys will be UTF-8 encoded. row to fetch. String keys will be UTF-8 encoded.
require_all_keys: Optional; If require_all_keys is True only require_all_keys: If True only rows with values set for all keys will be
rows with values set for all keys will be returned. returned.
Returns: Returns:
A dict mapping keys to the corresponding table row data A dict mapping keys to the corresponding table row data
@ -2115,8 +2133,7 @@ def fetch_smalltable_rows(table_handle: smalltable.Table,
A sequence of strings representing the key of each table row to A sequence of strings representing the key of each table row to
fetch. String keys will be UTF-8 encoded. fetch. String keys will be UTF-8 encoded.
require_all_keys: require_all_keys:
Optional; If require_all_keys is True only rows with values set If True only rows with values set for all keys will be returned.
for all keys will be returned.
Returns: Returns:
A dict mapping keys to the corresponding table row data A dict mapping keys to the corresponding table row data
@ -2283,7 +2300,7 @@ No: employee_table = '<table>'
Be consistent with your choice of string quote character within a file. Pick `'` Be consistent with your choice of string quote character within a file. Pick `'`
or `"` and stick with it. It is okay to use the other quote character on a or `"` and stick with it. It is okay to use the other quote character on a
string to avoid the need to `\\ ` escape within the string. string to avoid the need to backslash-escape quote characters within the string.
```python ```python
Yes: Yes:
@ -2678,22 +2695,33 @@ No:
<a id="s3.15-access-control"></a> <a id="s3.15-access-control"></a>
<a id="315-access-control"></a> <a id="315-access-control"></a>
<a id="access-control"></a> <a id="access-control"></a>
<a id="accessors"></a> <a id="accessors"></a>
### 3.15 Accessors
If an accessor function would be trivial, you should use public variables <a id="getters-and-setters"></a>
instead of accessor functions to avoid the extra cost of function calls in ### 3.15 Getters and Setters
Python. When more functionality is added you can use `property` to keep the
syntax consistent.
On the other hand, if access is more complex, or the cost of accessing the Getter and setter functions (also called accessors and mutators) should be used
variable is significant, you should use function calls (following the when they provide a meaningful role or behavior for getting or setting a
[Naming](#s3.16-naming) guidelines) such as `get_foo()` and `set_foo()`. If the variable's value.
past behavior allowed access through a property, do not bind the new accessor
functions to the property. Any code still attempting to access the variable by In particular, they should be used when getting or setting the variable is
the old method should break visibly so they are made aware of the change in complex or the cost is significant, either currently or in a reasonable future.
complexity.
If, for example, a pair of getters/setters simply read and write an internal
attribute, the internal attribute should be made public instead. By comparison,
if setting a variable means some state is invalidated or rebuilt, it should be a
setter function. The function invocation hints that a potentially non-trivial
operation is occurring. Alternatively, [properties](#properties) may be an
option when simple logic is needed, or refactoring to no longer need getters and
setters.
Getters and setters should follow the [Naming](#s3.16-naming) guidelines, such
as `get_foo()` and `set_foo()`.
If the past behavior allowed access through a property, do not bind the new
getter/setter functions to the property. Any code still attempting to access the
variable by the old method should break visibly so they are made aware of the
change in complexity.
<a id="s3.16-naming"></a> <a id="s3.16-naming"></a>
<a id="316-naming"></a> <a id="316-naming"></a>