coding-mentor-agent/kb/python-course-kb-practical-python/wiki/exercises/1-18-regular-expressions.md

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id	source_exercise_id	title	section	source_path	source_repo	source_commit	student_visible_solution	has_private_solution	skip
practical-python-1.18	1.18	Regular Expressions	1.4 Strings	01_Introduction/04_Strings.md	https://github.com/dabeaz-course/practical-python	93dca856b41c61a0a0f85ae334116e4c125629ea	false	false	false

Exercise 1.18: Regular Expressions

Source: Practical Python Programming, 01_Introduction/04_Strings.md.

Exercise 1.18: Regular Expressions

One limitation of the basic string operations is that they don't support any kind of advanced pattern matching. For that, you need to turn to Python's re module and regular expressions. Regular expression handling is a big topic, but here is a short example:

>>> text = 'Today is 3/27/2018. Tomorrow is 3/28/2018.'
>>> # Find all occurrences of a date
>>> import re
>>> re.findall(r'\d+/\d+/\d+', text)
['3/27/2018', '3/28/2018']
>>> # Replace all occurrences of a date with replacement text
>>> re.sub(r'(\d+)/(\d+)/(\d+)', r'\3-\1-\2', text)
'Today is 2018-3-27. Tomorrow is 2018-3-28.'
>>>

For more information about the re module, see the official documentation at https://docs.python.org/library/re.html.

Commentary

As you start to experiment with the interpreter, you often want to know more about the operations supported by different objects. For example, how do you find out what operations are available on a string?

Depending on your Python environment, you might be able to see a list of available methods via tab-completion. For example, try typing this:

>>> s = 'hello world'
>>> s.<tab key>
>>>

If hitting tab doesn't do anything, you can fall back to the builtin-in dir() function. For example:

>>> s = 'hello'
>>> dir(s)
['__add__', '__class__', '__contains__', ..., 'find', 'format',
'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace',
'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition',
'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit',
'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase',
'title', 'translate', 'upper', 'zfill']
>>>

dir() produces a list of all operations that can appear after the (.). Use the help() command to get more information about a specific operation:

>>> help(s.upper)
Help on built-in function upper:

upper(...)
    S.upper() -> string

    Return a copy of the string S converted to uppercase.
>>>

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关联来源

• summaries/04_Strings