114 lines
3.7 KiB
Python
114 lines
3.7 KiB
Python
# Tests against https://www.python.org/dev/peps/pep-0498/
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assert f'no interpolation' == 'no interpolation'
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assert f"no interpolation" == 'no interpolation'
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# Quoth the PEP:
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# Backslashes may not appear anywhere within expressions. Comments, using the
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# '#' character, are not allowed inside an expression
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#
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# CPython (3.7.4 on Linux) raises a SyntaxError here:
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# >>> f'{#}'
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# File "<stdin>", line 1
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# SyntaxError: f-string expression part cannot include '#'
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# >>> f'{\}'
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# File "<stdin>", line 1
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# SyntaxError: f-string expression part cannot include a backslash
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# >>> f'{\\}'
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# File "<stdin>", line 1
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# SyntaxError: f-string expression part cannot include a backslash
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# >>> f'{\#}'
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# File "<stdin>", line 1
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# SyntaxError: f-string expression part cannot include a backslash
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# Backslashes and comments allowed outside expression
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assert f"\\" == "\\"
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assert f'#' == '#'
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## But not inside
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try:
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eval("f'{\}'")
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except SyntaxError:
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pass
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else:
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raise AssertionError('f-string with backslash in expression did not raise SyntaxError')
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try:
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eval("f'{#}'")
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except SyntaxError:
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pass
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else:
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raise AssertionError('f-string with \'#\' in expression did not raise SyntaxError')
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# Quoth the PEP:
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# While scanning the string for expressions, any doubled braces '{{' or '}}'
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# inside literal portions of an f-string are replaced by the corresponding
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# single brace. Doubled literal opening braces do not signify the start of an
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# expression. A single closing curly brace '}' in the literal portion of a
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# string is an error: literal closing curly braces must be doubled '}}' in
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# order to represent a single closing brace.
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#
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# CPython (3.7.4 on Linux) raises a SyntaxError for the last case:
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# >>> f'{{}'
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# File "<stdin>", line 1
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# SyntaxError: f-string: single '}' is not allowed
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assert f'{{}}' == '{}'
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try:
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eval("f'{{}'")
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except ValueError:
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pass
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else:
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raise RuntimeError('Expected ValueError for invalid f-string literal bracing')
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x = 1
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assert f'{x}' == '1'
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# Quoth the PEP:
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# The expressions that are extracted from the string are evaluated in the
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# context where the f-string appeared. This means the expression has full
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# access to local and global variables. Any valid Python expression can be
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# used, including function and method calls. Because the f-strings are
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# evaluated where the string appears in the source code, there is no additional
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# expressiveness available with f-strings. There are also no additional
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# security concerns: you could have also just written the same expression, not
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# inside of an f-string:
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def foo():
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return 20
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assert f'result={foo()}' == 'result=20'
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assert f'result={foo()}' == 'result={}'.format(foo())
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assert f'result={foo()}' == 'result={result}'.format(result=foo())
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# Quoth the PEP:
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# Adjacent f-strings and regular strings are concatenated. Regular strings are
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# concatenated at compile time, and f-strings are concatenated at run time. For
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# example, the expression:
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#
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# >>> x = 10
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# >>> y = 'hi'
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# >>> 'a' 'b' f'{x}' '{c}' f'str<{y:^4}>' 'd' 'e'
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#
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# yields the value: 'ab10{c}str< hi >de'
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#
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# Because strings are concatenated at lexer time rather than parser time in
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# MicroPython for mostly RAM efficiency reasons (see
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# https://github.com/micropython/micropython/commit/534b7c368dc2af7720f3aaed0c936ef46d773957),
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# and because f-strings here are implemented as a syntax translation
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# (f'{something}' => '{}'.format(something)), this particular functionality is unimplemented,
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# and in the above example, the '{c}' portion will trigger a KeyError on String.format()
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x = 10
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y = 'hi'
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#assert (f'h' f'i') == 'hi'
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#assert (f'h' 'i') == 'hi'
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#assert ('h' f'i') == 'hi'
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assert f'{x:^4}' == ' 10 '
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#assert ('a' 'b' f'{x}' f'str<{y:^4}>' 'd' 'e') == 'ab10str< hi >de'
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# Other tests
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assert f'{{{4*10}}}' == '{40}'
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