请尝试：

import re

dicts = {"item1": "dog", "item2": "cat", "item4": "kindness"}

s = """This's my pet {item1|female donkey}. It was a gift from Mr {item3|David Smith}. Junior. I thank him for is {item4|humbleness}."""

pat = re.compile(r"\{([^|]+)\|([^}]+)}")
s = pat.sub(lambda g: dicts.get(g.group(1), g.group(2)), s)

print(s)

印刷品：

This's my pet dog. It was a gift from Mr David Smith. Junior. I thank him for is kindness.

编辑：如果没有提供默认项，您可以用途：

import re

dicts = {"item1": "dog", "item2": "cat", "item4": "kindness"}

s = """This's my pet {item1|female donkey}. It was a gift from Mr {item3|}. Junior. I thank him for is {item4|humbleness}."""

pat = re.compile(r"\{([^|]+)\|([^}]*)}")
s = pat.sub(lambda g: dicts.get(g.group(1), g.group(2).strip() or "N/A"), s)

print(s)

印刷品：

This's my pet dog. It was a gift from Mr N/A. Junior. I thank him for is kindness.