我不明白Pandas中子字符串的正确操作

import pandas as pd

df = pd.DataFrame({'text': ['hello world', 'foo bar', 'baz qux']})

# 检查是否包含子字符串'oo'
df['contains_oo'] = df['text'].str.contains('oo')

print(df)

          text  contains_oo
0  hello world         True
1      foo bar         True
2      baz qux        False

import pandas as pd

df = pd.DataFrame({'text': ['hello world', 'foo bar', 'baz qux']})

# 检查是否以子字符串'hello'开头
df['starts_with_hello'] = df['text'].str.startswith('hello')

# 检查是否以子字符串'bar'结束
df['ends_with_bar'] = df['text'].str.endswith('bar')

print(df)

          text  starts_with_hello  ends_with_bar
0  hello world               True          False
1      foo bar              False           True
2      baz qux              False          False

import pandas as pd

df = pd.DataFrame({'text': ['hello world', 'foo bar', 'baz qux']})

# 提取以字母'o'开头和以字母'r'结尾的子字符串
df['extracted'] = df['text'].str.extract(r'o(.*)r')

print(df)

          text extracted
0  hello world      wold
1      foo bar         b
2      baz qux      None

import pandas as pd

df = pd.DataFrame({'text': ['hello world', 'foo bar', 'baz qux']})

# 将子字符串'bar'替换为'qux'
df['replaced'] = df['text'].str.replace('bar', 'qux')

print(df)

          text     replaced
0  hello world  hello world
1      foo bar      foo qux
2      baz qux      baz qux