In Python, the `extract()` function is often used to extract specific patterns or matches from strings. It is implemented through regular expressions. The `extract()` function is usually called through the `Series` object of the `pandas` library, which is used to pattern match the strings in the Series and extract the matching parts.
Here's an example:
```python
import pandas as pd
data = pd.Series(["A1", "B2", "C3", "D4"])
# 使用正则表达式提取字母和数字
result = data.str.extract("([A-Z])(\d)")
print(result)
```
输出结果：
```
0 1
0 A 1
1 B 2
2 C 3
3 D 4
```In the above example, we extracted the alphanumeric portion of each string using the `extract()` function. The regular expression `([AZ])(\d)` is used to match a pattern of an uppercase letter followed by a number. The result of the extraction is a DataFrame containing two columns, where the first column (0) is the letter part and the second column (1) is the numeric part.
It should be noted that the `extract()` function returns a new DataFrame or Series object rather than modifying the original data.