Add fake f-strings to blurb. Works with 3.5! (#288)

Author: larryhastings

blurb/blurb.py

@@ -112,6 +112,32 @@
         sections.append(section.strip())
 
 
+def f(s):
+    """
+    Basic support for 3.6's f-strings, in 3.5!
+
+    Formats "s" using appropriate globals and locals
+    dictionaries.  This f-string:
+        f"hello a is {a}"
+    simply becomes
+        f("hello a is {a}")
+    In other words, just throw parentheses around the
+    string, and you're done!
+
+    Implemented internally using str.format_map().
+    This means it doesn't support expressions:
+        f("two minus three is {2-3}")
+    And it doesn't support function calls:
+        f("how many elements? {len(my_list)}")
+    But most other f-string features work.
+    """
+    frame = sys._getframe(1)
+    d = dict(builtins.__dict__)
+    d.update(frame.f_globals)
+    d.update(frame.f_locals)
+    return s.format_map(d)
+
+
 def sanitize_section(section):
     """
 Cleans up a section string, making it viable as a directory name.
@@ -224,10 +250,10 @@ def sortable_datetime():
 
 
 def prompt(prompt):
-    return input("[{}> ".format(prompt))
+    return input(f("[{prompt}> "))
 
 def require_ok(prompt):
-    prompt = "[{}> ".format(prompt)
+    prompt = f("[{prompt}> ")
     while True:
         s = input(prompt).strip()
         if s == 'ok':
@@ -457,7 +483,7 @@ def parse(self, text, *, metadata=None, filename="input"):
         line_number = None
 
         def throw(s):
-            raise BlurbError("Error in {}:{}:\n{}".format(filename, line_number, s))
+            raise BlurbError(f("Error in {filename}:{line_number}:\n{s}"))
 
         def finish_entry():
             nonlocal body
@@ -522,8 +548,8 @@ def load(self, filename, *, metadata=None):
 
 Broadly equivalent to blurb.parse(open(filename).read()).
         """
-        with open(filename, "rt", encoding="utf-8") as f:
-            text = f.read()
+        with open(filename, "rt", encoding="utf-8") as file:
+            text = file.read()
         self.parse(text, metadata=metadata, filename=filename)
 
     def __str__(self):
@@ -537,7 +563,7 @@ def __str__(self):
                 add_separator = True
             if metadata:
                 for name, value in sorted(metadata.items()):
-                    add(".. {}: {}\n".format(name, value))
+                    add(f(".. {name}: {value}\n"))
                 add("\n")
             add(textwrap_body(body))
         return "".join(output)
@@ -547,8 +573,8 @@ def save(self, path):
         safe_mkdir(dirname)
 
         text = str(self)
-        with open(path, "wt", encoding="utf-8") as f:
-            f.write(text)
+        with open(path, "wt", encoding="utf-8") as file:
+            file.write(text)
 
     @staticmethod
     def _parse_next_filename(filename):
@@ -559,10 +585,10 @@ def _parse_next_filename(filename):
         components = filename.split(os.sep)
         section, filename = components[-2:]
         section = unsanitize_section(section)
-        assert section in sections, "Unknown section {}".format(section)
+        assert section in sections, f("Unknown section {section}")
 
         fields = [x.strip() for x in filename.split(".")]
-        assert len(fields) >= 4, "Can't parse 'next' filename! filename {!r} fields {}".format(filename, fields)
+        assert len(fields) >= 4, f("Can't parse 'next' filename! filename {filename!r} fields {fields}")
         assert fields[-1] == "rst"
 
         metadata = {"date": fields[0], "nonce": fields[-2], "section": section}
@@ -656,8 +682,8 @@ def filename_test(self, filename):
         b.load(filename)
         self.assertTrue(b)
         if os.path.exists(filename + '.res'):
-            with open(filename + '.res', encoding='utf-8') as f:
-                expected = f.read()
+            with open(filename + '.res', encoding='utf-8') as file:
+                expected = file.read()
             self.assertEqual(str(b), expected)
 
     def test_files(self):
@@ -712,8 +738,8 @@ def chdir_to_repo_root():
         def test_first_line(filename, test):
             if not os.path.exists(filename):
                 return False
-            with open(filename, "rt") as f:
-                lines = f.read().split('\n')
+            with open(filename, "rt") as file:
+                lines = file.read().split('\n')
                 if not (lines and test(lines[0])):
                     return False
             return True
@@ -751,7 +777,7 @@ def subcommand(fn):
 def get_subcommand(subcommand):
     fn = subcommands.get(subcommand)
     if not fn:
-        error("Unknown subcommand: {}\nRun 'blurb help' for help.".format(subcommand))
+        error(f("Unknown subcommand: {subcommand}\nRun 'blurb help' for help."))
     return fn
 
 
@@ -813,19 +839,19 @@ def help(subcommand=None):
     for name, p in inspect.signature(fn).parameters.items():
         if p.kind == inspect.Parameter.KEYWORD_ONLY:
             short_option = name[0]
-            options.append(" [-{}|--{}]".format(short_option, name))
+            options.append(f(" [-{short_option}|--{name}]"))
         elif p.kind == inspect.Parameter.POSITIONAL_OR_KEYWORD:
             positionals.append(" ")
             has_default = (p.default != inspect._empty)
             if has_default:
                 positionals.append("[")
                 nesting += 1
-            positionals.append("<{}>".format(name))
+            positionals.append(f("<{name}>"))
     positionals.append("]" * nesting)
 
 
     parameters = "".join(options + positionals)
-    print("blurb {}{}".format(subcommand, parameters))
+    print(f("blurb {subcommand}{parameters}"))
     print()
     print(doc)
     sys.exit(0)
@@ -888,7 +914,7 @@ def add():
     atexit.register(lambda : os.unlink(tmp_path))
 
     def init_tmp_with_template():
-        with open(tmp_path, "wt", encoding="utf-8") as f:
+        with open(tmp_path, "wt", encoding="utf-8") as file:
             # hack:
             # my editor likes to strip trailing whitespace from lines.
             # normally this is a good idea.  but in the case of the template
@@ -902,7 +928,7 @@ def init_tmp_with_template():
             if without_space not in text:
                 sys.exit("Can't find BPO line to ensure there's a space on the end!")
             text = text.replace(without_space, with_space)
-            f.write(text)
+            file.write(text)
 
     init_tmp_with_template()
 
@@ -916,7 +942,7 @@ def init_tmp_with_template():
     else:
         args = list(shlex.split(editor))
         if not shutil.which(args[0]):
-            sys.exit("Invalid GIT_EDITOR / EDITOR value: {}".format(editor))
+            sys.exit(f("Invalid GIT_EDITOR / EDITOR value: {editor}"))
     args.append(tmp_path)
 
     while True:
@@ -936,7 +962,7 @@ def init_tmp_with_template():
 
         if failure:
             print()
-            print("Error: {}".format(failure))
+            print(f("Error: {failure}"))
             print()
             try:
                 prompt("Hit return to retry (or Ctrl-C to abort)")
@@ -970,20 +996,20 @@ def release(version):
     if existing_filenames:
         error("Sorry, can't handle appending 'next' files to an existing version (yet).")
 
-    output = "Misc/NEWS.d/{}.rst".format(version)
+    output = f("Misc/NEWS.d/{version}.rst")
     filenames = glob_blurbs("next")
     blurbs = Blurbs()
     date = current_date()
 
     if not filenames:
-        print("No blurbs found.  Setting {} as having no changes.".format(version))
-        body = "There were no new changes in version {}.\n".format(version)
+        print(f("No blurbs found.  Setting {version} as having no changes."))
+        body = f("There were no new changes in version {version}.\n")
         metadata = {"no changes": "True", "bpo": "0", "section": "Library", "date": date, "nonce": nonceify(body)}
         blurbs.append((metadata, body))
     else:
         no_changes = None
         count = len(filenames)
-        print('Merging {} blurbs to "{}".'.format(count, output))
+        print(f('Merging {count} blurbs to "{output}".'))
 
         for filename in filenames:
             if not filename.endswith(".rst"):
@@ -999,14 +1025,15 @@ def release(version):
     git_add_files.append(output)
     flush_git_add_files()
 
-    print("Removing {} 'next' files from git.".format(len(filenames)))
+    how_many = len(filenames)
+    print(f("Removing {how_many} 'next' files from git."))
     git_rm_files.extend(filenames)
     flush_git_rm_files()
 
     # sanity check: ensuring that saving/reloading the merged blurb file works.
     blurbs2 = Blurbs()
     blurbs2.load(output)
-    assert blurbs2 == blurbs, "Reloading {} isn't reproducible?!".format(output)
+    assert blurbs2 == blurbs, f("Reloading {output} isn't reproducible?!")
 
     print()
     print("Ready for commit.")
@@ -1077,7 +1104,7 @@ def print(*a, sep=" "):
         metadata, body = blurbs[0]
         release_date = metadata["release date"]
 
-        print("*Release date: {}*".format(release_date))
+        print(f("*Release date: {release_date}*"))
         print()
 
         if "no changes" in metadata:
@@ -1145,11 +1172,11 @@ def populate():
 
     for section in sections:
         dir_name = sanitize_section(section)
-        dir_path = "NEWS.d/next/{}".format(dir_name)
+        dir_path = f("NEWS.d/next/{dir_name}")
         safe_mkdir(dir_path)
-        readme_path = "NEWS.d/next/{}/README.rst".format(dir_name)
-        with open(readme_path, "wt", encoding="utf-8") as f:
-            f.write("Put news entry ``blurb`` files for the *{}* section in this directory.\n".format(section))
+        readme_path = f("NEWS.d/next/{dir_name}/README.rst")
+        with open(readme_path, "wt", encoding="utf-8") as readme:
+            readme.write(f("Put news entry ``blurb`` files for the *{section}* section in this directory.\n"))
         git_add_files.append(dir_path)
         git_add_files.append(readme_path)
     flush_git_add_files()
@@ -1170,7 +1197,7 @@ def export():
 #    """
 #    Test function for blurb command-line processing.
 #    """
-#    print("arg: boolean {} option {}".format(boolean, option))
+#    print(f("arg: boolean {boolean} option {option}"))
 
 
 @subcommand
@@ -1255,7 +1282,7 @@ def flush_blurb():
                         fields.append(field)
                     see_also = ", ".join(fields)
                     # print("see_also: ", repr(see_also))
-                    accumulator.append("(See also: {})".format(see_also))
+                    accumulator.append(f("(See also: {see_also})"))
                     see_also = None
                 if not accumulator:
                     return
@@ -1301,8 +1328,8 @@ def flush_version():
         if version is None:
             assert not blurbs, "version should only be None initially, we shouldn't have blurbs yet"
             return
-        assert blurbs, "No blurbs defined when flushing version {}!".format(version)
-        output = "NEWS.d/{}.rst".format(version)
+        assert blurbs, f("No blurbs defined when flushing version {version}!")
+        output = f("NEWS.d/{version}.rst")
 
         if released:
             # saving merged blurb file for version, e.g. Misc/NEWS.d/3.7.0a1.rst
@@ -1318,8 +1345,8 @@ def flush_version():
         blurbs.clear()
         version_count += 1
 
-    with open("NEWS", "rt", encoding="utf-8") as f:
-        for line_number, line in enumerate(f):
+    with open("NEWS", "rt", encoding="utf-8") as file:
+        for line_number, line in enumerate(file):
             line = line.rstrip()
 
             if line.startswith("\ufeff"):
@@ -1420,11 +1447,11 @@ def flush_version():
             elif line.startswith("- Issue #9516: Issue #9516: avoid errors in sysconfig when MACOSX_DEPLOYMENT_TARGET"):
                 line = "- Issue #9516 and Issue #9516: avoid errors in sysconfig when MACOSX_DEPLOYMENT_TARGET"
             elif line.title().startswith(("- Request #", "- Bug #", "- Patch #", "- Patches #")):
-                # print("FIXING LINE {}: {!r}".format(line_number), line)
+                # print(f("FIXING LINE {line_number}: {line!r}"))
                 line = "- Issue #" + line.partition('#')[2]
-                # print("FIXED LINE {!r}".format(line))
+                # print(f("FIXED LINE {line_number}: {line!r}"))
             # else:
-            #     print("NOT FIXING LINE {}: {!r}".format(line_number, line))
+            #     print(f("NOT FIXING LINE {line_number}: {line!r}"))
 
 
             # 4. determine the actual content of the line
@@ -1489,7 +1516,7 @@ def flush_version():
                     line = line[4:]
                     parse_bpo = True
                 else:
-                    # print("[[{:8} no bpo]] {}".format(line_number, line))
+                    # print(f("[[{line_number:8} no bpo]] {line}"))
                     parse_bpo = False
                 if parse_bpo:
                     # GAAAH
@@ -1529,9 +1556,9 @@ def flush_version():
                     try:
                         int(bpo) # this will throw if it's not a legal int
                     except ValueError:
-                        sys.exit("Couldn't convert bpo number to int on line {}! ".format(line_number) + repr(bpo))
+                        sys.exit(f("Couldn't convert bpo number to int on line {line_number}! {bpo!r}"))
                     if see_also == "partially":
-                        sys.exit("What the hell on line {}! ".format(line_number) + repr(bpo))
+                        sys.exit(f("What the hell on line {line_number}! {bpo!r}"))
 
             # 4.6.1 continuation of blurb
             elif line.startswith("  "):
@@ -1540,7 +1567,7 @@ def flush_version():
             elif line.startswith(" * "):
                 line = line[3:]
             elif line:
-                sys.exit("Didn't recognize line {}! ".format(line_number) + repr(line))
+                sys.exit(f("Didn't recognize line {line_number}! {line!r}"))
             # only add blank lines if we have an initial line in the accumulator
             if line or accumulator:
                 accumulator.append(line)
@@ -1552,7 +1579,7 @@ def flush_version():
     git_rm_files.append("NEWS")
     flush_git_rm_files()
 
-    print("Wrote {} news items across {} versions.".format(blurb_count, version_count))
+    print(f("Wrote {blurb_count} news items across {version_count} versions."))
     print()
     print("Ready for commit.")
 
@@ -1601,10 +1628,10 @@ def main():
         def handle_option(s, dict):
             name = dict.get(s, None)
             if not name:
-                sys.exit('blurb: Unknown option for {}: "{}"'.format(subcommand, s))
+                sys.exit(f('blurb: Unknown option for {subcommand}: "{s}"'))
             kwargs[name] = not kwargs[name]
 
-        # print("short_options {} long_options {}".format(short_options, long_options))
+        # print(f("short_options {short_options} long_options {long_options}"))
         for a in args:
             if done_with_options:
                 filtered_args.append(a)
@@ -1638,7 +1665,7 @@ def handle_option(s, dict):
             # whoops, must be a real type error, reraise
             raise e
 
-        how_many = "{} argument".format(specified)
+        how_many = f("{specified} argument")
         if specified != 1:
             how_many += "s"
 
@@ -1649,12 +1676,12 @@ def handle_option(s, dict):
                 middle = "requires"
             else:
                 plural = "" if required == 1 else "s"
-                middle = "requires at least {} argument{} and at most".format(required, plural)
-            middle += " {} argument".format(total)
+                middle = f("requires at least {required} argument{plural} and at most")
+            middle += f(" {total} argument")
             if total != 1:
                 middle += "s"
 
-        print('Error: Wrong number of arguments!\n\nblurb {} {},\nand you specified {}.'.format(subcommand, middle, how_many))
+        print(f('Error: Wrong number of arguments!\n\nblurb {subcommand} {middle},\nand you specified {how_many}.'))
         print()
         print("usage: ", end="")
         help(subcommand)