pandas code style guide¶

Table of contents:

Patterns
- foo.__class__
String formatting
- Concatenated strings
  - f-strings
  - White spaces
- Representation function (aka ‘repr()’)
Imports (aim for absolute)

Patterns ¶

foo.class¶

pandas uses ‘type(foo)’ instead ‘foo.__class__’ as it is making the code more readable.

For example:

Good:

foo = "bar"
type(foo)

Bad:

foo = "bar"
foo.__class__

String formatting ¶

Concatenated strings ¶

f-strings ¶

pandas uses f-strings formatting instead of ‘%’ and ‘.format()’ string formatters.

The convention of using f-strings on a string that is concatenated over serveral lines, is to prefix only the lines containing the value needs to be interpeted.

For example:

Good:

foo = "old_function"
bar = "new_function"

my_warning_message = (
    f"Warning, {foo} is deprecated, "
    "please use the new and way better "
    f"{bar}"
)

Bad:

foo = "old_function"
bar = "new_function"

my_warning_message = (
    f"Warning, {foo} is deprecated, "
    f"please use the new and way better "
    f"{bar}"
)

White spaces ¶

Putting the white space only at the end of the previous line, so there is no whitespace at the beggining of the concatenated string.

For example:

Good:

example_string = (
    "Some long concatenated string, "
    "with good placement of the "
    "whitespaces"
)

Bad:

example_string = (
    "Some long concatenated string,"
    " with bad placement of the"
    " whitespaces"
)

Representation function (aka ‘repr()’)¶

pandas uses ‘repr()’ instead of ‘%r’ and ‘!r’.

The use of ‘repr()’ will only happend when the value is not an obvious string.

For example:

Good:

value = str
f"Unknown recived value, got: {repr(value)}"

Good:

value = str
f"Unknown recived type, got: '{type(value).__name__}'"

In Python 3, absolute imports are recommended. In absolute import doing something like import string will import the string module rather than string.py in the same directory. As much as possible, you should try to write out absolute imports that show the whole import chain from toplevel pandas.

Explicit relative imports are also supported in Python 3. But it is not recommended to use it. Implicit relative imports should never be used and is removed in Python 3.

For example:

# preferred
import pandas.core.common as com

# not preferred
from .common import test_base

# wrong
from common import test_base