Merge pull request #2 from adafruit/master

Master

1 files changed, 113 insertions, 0 deletions

diff --git a/tests/basics/string_pep498_fstring.py b/tests/basics/string_pep498_fstring.py
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+++ b/tests/basics/string_pep498_fstring.py
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+# Tests against https://www.python.org/dev/peps/pep-0498/
+
+assert f'no interpolation' == 'no interpolation'
+assert f"no interpolation" == 'no interpolation'
+
+# Quoth the PEP:
+# Backslashes may not appear anywhere within expressions. Comments, using the
+# '#' character, are not allowed inside an expression
+#
+# CPython (3.7.4 on Linux) raises a SyntaxError here:
+# >>> f'{#}'
+#   File "<stdin>", line 1
+# SyntaxError: f-string expression part cannot include '#'
+# >>> f'{\}'
+#   File "<stdin>", line 1
+# SyntaxError: f-string expression part cannot include a backslash
+# >>> f'{\\}'
+#   File "<stdin>", line 1
+# SyntaxError: f-string expression part cannot include a backslash
+# >>> f'{\#}'
+#   File "<stdin>", line 1
+# SyntaxError: f-string expression part cannot include a backslash
+
+# Backslashes and comments allowed outside expression
+assert f"\\" == "\\"
+assert f'#' == '#'
+
+## But not inside
+try:
+    eval("f'{\}'")
+except SyntaxError:
+    pass
+else:
+    raise AssertionError('f-string with backslash in expression did not raise SyntaxError')
+
+try:
+    eval("f'{#}'")
+except SyntaxError:
+    pass
+else:
+    raise AssertionError('f-string with \'#\' in expression did not raise SyntaxError')
+
+# Quoth the PEP:
+# While scanning the string for expressions, any doubled braces '{{' or '}}'
+# inside literal portions of an f-string are replaced by the corresponding
+# single brace.  Doubled literal opening braces do not signify the start of an
+# expression. A single closing curly brace '}' in the literal portion of a
+# string is an error: literal closing curly braces must be doubled '}}' in
+# order to represent a single closing brace.
+#
+# CPython (3.7.4 on Linux) raises a SyntaxError for the last case:
+# >>> f'{{}'
+#   File "<stdin>", line 1
+# SyntaxError: f-string: single '}' is not allowed
+
+assert f'{{}}' == '{}'
+
+try:
+    eval("f'{{}'")
+except ValueError:
+    pass
+else:
+    raise RuntimeError('Expected ValueError for invalid f-string literal bracing')
+
+x = 1
+assert f'{x}' == '1'
+
+# Quoth the PEP:
+# The expressions that are extracted from the string are evaluated in the
+# context where the f-string appeared. This means the expression has full
+# access to local and global variables. Any valid Python expression can be
+# used, including function and method calls.  Because the f-strings are
+# evaluated where the string appears in the source code, there is no additional
+# expressiveness available with f-strings. There are also no additional
+# security concerns: you could have also just written the same expression, not
+# inside of an f-string:
+
+def foo():
+    return 20
+
+assert f'result={foo()}' == 'result=20'
+assert f'result={foo()}' == 'result={}'.format(foo())
+assert f'result={foo()}' == 'result={result}'.format(result=foo())
+
+
+# Quoth the PEP:
+# Adjacent f-strings and regular strings are concatenated. Regular strings are
+# concatenated at compile time, and f-strings are concatenated at run time. For
+# example, the expression:
+#
+# >>> x = 10
+# >>> y = 'hi'
+# >>> 'a' 'b' f'{x}' '{c}' f'str<{y:^4}>' 'd' 'e'
+#
+# yields the value: 'ab10{c}str< hi >de'
+#
+# Because strings are concatenated at lexer time rather than parser time in
+# MicroPython for mostly RAM efficiency reasons (see
+# https://github.com/micropython/micropython/commit/534b7c368dc2af7720f3aaed0c936ef46d773957),
+# and because f-strings here are implemented as a syntax translation
+# (f'{something}' => '{}'.format(something)), this particular functionality is unimplemented,
+# and in the above example, the '{c}' portion will trigger a KeyError on String.format()
+
+x = 10
+y = 'hi'
+assert (f'h' f'i') == 'hi'
+#assert (f'h' 'i') == 'hi'
+#assert ('h' f'i') == 'hi'
+assert f'{x:^4}' == ' 10 '
+#assert ('a' 'b' f'{x}' f'str<{y:^4}>' 'd' 'e') == 'ab10str< hi >de'
+
+# Other tests
+assert f'{{{4*10}}}' == '{40}'