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48 lines
1.3 KiB
Markdown
48 lines
1.3 KiB
Markdown
# Escape Curly Braces Within Formatted String
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Python's
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[_f-string_](https://docs.python.org/3/reference/lexical_analysis.html#f-strings)
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allows you to interpolate values into a string literal like so:
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```python
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>>> amount = 25
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>>> print(f"Price: ${amount}")
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Price: $25
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```
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The `{` and `}` are betting special treatment when `f` precedes the string
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literal. So, what if the resulting string is supposed to have literal `{` and
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`}` characters in it?
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```python
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>>> f"JSON opens and closes with curlies: {...}"
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'JSON opens and closes with curlies: Ellipsis'
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```
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I need a way of escaping them. The trick is to double them up.
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```python
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>>> f"JSON opens and closes with curlies: {{...}}"
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'JSON opens and closes with curlies: {...}'
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```
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A more practical example of where this is useful is in formatting an expected
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string of JSON in a test:
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```python
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info_result = runner.invoke(cli, ["info", "--json"])
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output = textwrap.dedent(f"""
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{{
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"config_file": "{config_file}",
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"data_dir": "{data_dir}",
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"version": "{VMT_VERSION}",
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"schema_version": 1
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}}
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""").strip()
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assert output in info_result.output
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```
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I'm doing some interpolation at various points in the string literal, but the
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outer curly braces are meant to be literal, the opening and closing of the JSON
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object.
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