python常用模块之string

本文简单介绍了 python 中字符串类 string，包括 constants、Formatter 和 Template。

str 是 built-in string class，string 是 A collection of string constants。

help#

模块 string 定义了一些字符类型集常量：

# 或直接输入 help('string')
>>> import string
>>> print(string.__doc__)
A collection of string constants.

Public module variables:

whitespace -- a string containing all ASCII whitespace
ascii_lowercase -- a string containing all ASCII lowercase letters
ascii_uppercase -- a string containing all ASCII uppercase letters
ascii_letters -- a string containing all ASCII letters
digits -- a string containing all ASCII decimal digits
hexdigits -- a string containing all ASCII hexadecimal digits
octdigits -- a string containing all ASCII octal digits
punctuation -- a string containing all ASCII punctuation characters
printable -- a string containing all ASCII characters considered printable

>>> string.digits
'0123456789'
>>> '5' in string.digits
True

>>> string.hexdigits
'0123456789abcdefABCDEF'
>>> 'f' in string.hexdigits
True

Formatter#

Custom String Formatting

The built-in string class provides the ability to do complex variable substitutions and value formatting via the format() method described in PEP 3101.
The Formatter class in the string module allows you to create and customize your own string formatting behaviors using the same implementation as the built-in format() method.

class string.Formatter
The Formatter class has the following public methods:

format(format_string, *args, **kwargs)
    The primary API method. It takes a format string and an arbitrary set of positional and keyword arguments. It is just a wrapper that calls vformat().

vformat(format_string, args, kwargs)
    This function does the actual work of formatting. It is exposed as a separate function for cases where you want to pass in a predefined dictionary of arguments, rather than unpacking and repacking the dictionary as individual arguments using the *args and **kwargs syntax.

Template#

CLASSES
    builtins.object
        Formatter
        Template

The string module provides a Template class that implements these rules. The methods of Template are:

class string.Template(template)

The constructor takes a single argument which is the template string.

>>> from string import Template
>>> s = Template('$who likes $what')
>>> s.substitute(who='tim', what='kung pao')
'tim likes kung pao'

TDW（腾讯的分布式数据仓库） HIVE SQL 使用了 python 作为流程控制语言，以下摘自某段格式化查询脚本：

# 模板（大括号可省略）
sql_query_t = 'SELECT * FROM ${db}::${tbl} WHERE time=${date}'
# 格式化替换参数
sql_query = string.Template(sql_query_t).substitute(db='myDB', tbl='myTable', date='20180108')
# 执行 sql
tdwqe.execute(sql_query)

python常用模块之string

help#

Formatter#

Template#

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