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

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+---
+id: practical-python-1.18
+source_exercise_id: "1.18"
+title: "Regular Expressions"
+section: "1.4 Strings"
+source_path: "01_Introduction/04_Strings.md"
+source_repo: "https://github.com/dabeaz-course/practical-python"
+source_commit: "93dca856b41c61a0a0f85ae334116e4c125629ea"
+student_visible_solution: false
+has_private_solution: false
+skip: 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:
+
+```python
+>>> 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](https://docs.python.org/3/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:
+
+```python
+>>> 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:
+
+```python
+>>> 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:
+
+```python
+>>> help(s.upper)
+Help on built-in function upper:
+
+upper(...)
+    S.upper() -> string
+
+    Return a copy of the string S converted to uppercase.
+>>>
+```
+
+[Contents](../Contents.md) \| [Previous (1.3 Numbers)](03_Numbers.md) \| [Next (1.5 Lists)](05_Lists.md)
+
+## 关联来源
+
+- [[summaries/04_Strings]]