Python

Doc: https://docs.python.org/dev/tutorial/index.html

datetime

datetime

A datetime object is a single object containing all the information from a date object and a time object.

[ins] In [27]: from datetime import datetime, timedelta

[ins] In [31]: dt = datetime.now()

[ins] In [32]: dt
Out[32]: datetime.datetime(2024, 8, 20, 14, 10, 8, 566237)

[ins] In [33]: dt.strftime("%Y-%m-%d %H:%M:%S")
Out[33]: '2024-08-20 14:10:08'

[ins] In [34]: datetime.strptime("20240820", "%Y%m%d")
Out[34]: datetime.datetime(2024, 8, 20, 0, 0)

Method	strftime	strptime
Usage	Convert object to a string according to a given format	Parse a string into a datetime object given a corresponding format
Type of method	Instance method	Class method
Method of	date; datetime; time	datetime
Signature	strftime(format)	strptime(date_string, format)

timedelta

A timedelta object represents a duration, the difference between two datetime or date instances.

[ins] In [27]: from datetime import datetime, timedelta

[ins] In [28]: now = datetime.now()

[ins] In [29]: timedelta(days=365)
Out[29]: datetime.timedelta(days=365)

[ins] In [30]: now - timedelta(days=365)
Out[30]: datetime.datetime(2023, 8, 21, 14, 8, 22, 953271)

sys

1. sys.byteorder: An indicator of the native byte order. Edianness output little or big.

fileinput

1. Create an instance of the FileInput class.

   使用readline()方法读取一行输入：

   >>> import fileinput
   >>> stdin = fileinput.input()
   >>> stdin.readline()
   hello world
   'hello world\n'
   >>> stdin.readline()
   
   '\n'
   

Built-in Functions

1. exec(): This function supports dynamic execution of Python code. object must be either a string or a code object. If it is a string, the string is parsed as a suite of Python statements which is then executed (unless a syntax error occurs).

   输入一行字符串并作为 Python 语句执行：

   >>> import fileinput
   >>> stdin = fileinput.input()
   >>> exec(stdin.readline())
   x = 1; y = 2;
   >>> x, y
   (1, 2)
   >>> exec(stdin.readline())
   arr = [1, 2, 3, 4, 5]
   >>> arr
   [1, 2, 3, 4, 5]
   

2. globals(): Return a dictionary representing the current global symbol table. This is always the dictionary of the current module (inside a function or method, this is the module where it is defined, not the module from which it is called).

   全局符号表

   >>> a, b, c = 1, 2, 3
   >>> globals()['a'] = -1
   >>> globals()
   {'__name__': '__main__', '__doc__': None, '__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__spec__': None, '__annotations__': {}, '__builtins__': <module 'builtins' (built-in)>, 'a': -1, 'b': 2, 'c': 3}
   

3. ord(c): Given a string representing one Unicode character, return an integer representing the Unicode code point of that character c. chr(i): Return the string representing a character whose Unicode code point is the integer i.

   Unicode 字符与编码相互转换

   >>> ord('a'), chr(97), ord('0'), chr(48)
   (97, 'a', 48, '0')
   

4. format(value[, format_spec]): Convert a value to a “formatted” representation, as controlled by format_spec. bin(x): Convert an integer number to a binary string prefixed with “0b”. oct(x): Convert an integer number to an octal string prefixed with “0o”. hex(x): Convert an integer number to a lowercase hexadecimal string prefixed with “0x”.

   >>> bin(14), oct(14), hex(14)
   ('0b1110', '0o16', '0xe')
   >>> format(14, '#b'), format(14, 'b')
   ('0b1110', '1110')
   >>> f'{14:#b}', f'{14:b}'
   ('0b1110', '1110')
   >>> f'{14:#x}', f'{14:x}'
   ('0xe', 'e')
   >>> f'{14:#o}', f'{14:o}'
   ('0o16', '16')
   

IPython Tips

1. 如果你不确定 function, class, or method 的使用方法，打印 __doc__ 属性，查看文档，或者在 IPython 中语句末尾加上一个 question mark ? ，两个 ?? 查看更详细的内容

   In [17]: print(spark.read.__doc__)
   
       Interface used to load a :class:`DataFrame` from external storage systems
       (e.g. file systems, key-value stores, etc). Use :attr:`SparkSession.read`
       to access this.
   
       .. versionadded:: 1.4.0
   
       .. versionchanged:: 3.4.0
           Supports Spark Connect.
   
   
   In [18]: spark.read?
   Type:        property
   String form: <property object at 0x104841b20>
   Docstring:
   Returns a :class:`DataFrameReader` that can be used to read data
   in as a :class:`DataFrame`.
   
   .. versionadded:: 2.0.0
   
   .. versionchanged:: 3.4.0
       Supports Spark Connect.
   
   Returns
   -------
   :class:`DataFrameReader`
   
   Examples
   --------
   >>> spark.read
   <...DataFrameReader object ...>
   
   Write a DataFrame into a JSON file and read it back.
   
   >>> import tempfile
   >>> with tempfile.TemporaryDirectory() as d:
   ...     # Write a DataFrame into a JSON file
   ...     spark.createDataFrame(
   ...         [{"age": 100, "name": "Hyukjin Kwon"}]
   ...     ).write.mode("overwrite").format("json").save(d)
   ...
   ...     # Read the JSON file as a DataFrame.
   ...     spark.read.format('json').load(d).show()
   +---+------------+
   |age|        name|
   +---+------------+
   |100|Hyukjin Kwon|
   +---+------------+
   

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