Coding Style Guidline.rst

Coding Style Guidline.rst

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+pandas Coding Style Guide
+=========================
+
+1 Background
+------------
+
+Writing good code is not just about what you write. It is also about how
+you write it. During Continuous Integration testing, several tools will
+be run to check your code for stylistic errors. Generating any warnings
+will cause the test to fail. Thus, good style is a requirement for
+submitting code to *pandas*. This document serves as a supplement to the
+script demonstrating the proper coding style required for contributing
+to *pandas*.
+
+2 Patterns
+----------
+
+2.1 Line Length
+~~~~~~~~~~~~~~~
+
+Line length is restricted to 80 characters to promote readability.
+
+2.2 Indentation
+~~~~~~~~~~~~~~~
+
+Indentations must be multiples of 4
+
+For example:
+
+**Good:**
+
+::       
+
+    if i == 0
+        if x == 3
+            x = 10
+
+**Bad:**
+
+::   
+
+  if i == 0
+    if x == 3
+     x = 10
+
+2.3 Whitespaces Around Arithmetic Operators
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There must be whitespaces surrounding arithmetic operators
+
+**Good:**
+
+::
+
+   x = 3 + 5 / 2
+
+**Bad:**
+
+::
+
+   x=3+5/2
+
+2.4 Missing White Spaces After Commas
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There must be a whitespace following a comma
+
+**Good:**
+
+::
+
+   myFunctionCall('a', 'b', 'c')
+
+**Bad:**
+
+::
+
+   myFunctionCall('a','b','c')
+
+2.5 Header File
+~~~~~~~~~~~~~~~
+
+Every header file must include a header guard to avoid name collision if
+re-included.
+
+2.6 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__
+
+2.7 Bare Pytest Raises
+~~~~~~~~~~~~~~~~~~~~~~
+
+**Good:**
+
+::
+
+   with pytest.raise(ValueError, match="foo"):
+       # following code that raises ValueError
+
+**Bad:**
+
+::
+
+   with pytest.raise(ValueError):
+       # following code that raises ValueError
+
+3 String Formatting
+-------------------
+
+3.1 Concatenated Strings
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+3.1.1 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}"
+   )
+
+3.1.2 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"
+   )
+
+3.2 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)}"
+
+**Bad:**
+
+::
+
+   value = str
+   f"Unknown recived type, got: '{type(value).__name__}'"
+
+4 Types
+-------
+
+**pandas** strongly encourages the use of PEP 484 style type hints. New
+development should contain type hints and pull requests to annotate
+existing code are accepted as well!
+
+4.1 Imports
+~~~~~~~~~~~
+
+Types imports should follow the ``from typing import ...`` convention.
+
+**Good:**
+
+::
+
+   from typing import List, Optional, Union
+
+   primes: List[int] = []
+
+**Bad:**
+
+::
+
+   import typing
+
+   primes: typing.List[int] = []
+
+Optional should be used where applicable
+
+**Good:**
+
+::
+
+   maybe_primes: List[Optional[int]] = []
+
+**Bad:**
+
+::
+
+   maybe_primes: List[Union[int, None]] = []
+
+4.1.1 Redundant Imports
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Should not import numpy and pandas
+
+**Example:**
+
+::
+
+   import numpy as np
+   import pandas as pd
+
+4.1.2 Unused Imports
+^^^^^^^^^^^^^^^^^^^^
+
+Unused imports must be removed prior to submission
+
+**Example:**
+
+::
+
+   import pandas as pdf
+   df = pd.DataFrame(np.ones((3, 3)), columns=('a', 'b', 'c'))