Framework code for compilerlike scripts.

Lib/compilerlike.py

@@ -0,0 +1,154 @@
+"""
+compilerlike -- framework code for building compiler-like programs.
+
+There is a common `compiler-like' pattern in Unix scripts which is useful
+for translation utilities of all sorts.  A program following this pattern
+behaves as a filter when no argument files are specified on the command
+line, but otherwise transforms each file individually into a corresponding
+output file.
+
+This module provides framework and glue code to make such programs easy
+to write.  You supply a function to massage the file data; depending
+on which entry point you use, it can take input and output file pointers,
+or it can take a string consisting of the entire file's data and return
+a replacement, or it can take in succession strings consisting of each
+of the file's lines and return a translated line for each.
+
+Argument files are transformed in left to right order in the argument list.
+A filename consisting of a dash is interpreted as a directive to read from
+standard input (this can be useful in pipelines).
+
+Replacement of each file is atomic and doesn't occur until the
+translation of that file has completed.  Any tempfiles are removed
+automatically on any exception thrown by the translation function,
+and the exception is then passed upwards.
+"""
+
+# Requires Python 2.
+from __future__ import nested_scopes
+
+import sys, os, filecmp, traceback
+
+def filefilter(name, arguments, trans_data, trans_filename=None):
+    "Filter stdin to stdout, or file arguments to renamed files."
+    if not arguments:
+        trans_data("stdin", sys.stdin, sys.stdout)
+    else:
+        for file in arguments:
+            if file == '-':		# - is conventional for stdin
+                file = "stdin"
+                infp = sys.stdin
+            else:
+                infp = open(file)
+            tempfile = file + ".~%s-%d~" % (name, os.getpid())
+            outfp = open(tempfile, "w")
+            try:
+                trans_data(file, infp, outfp)
+            except:
+                os.remove(tempfile)
+                # Pass the exception upwards
+                (exc_type, exc_value, exc_traceback) = sys.exc_info()
+                raise exc_type, exc_value, exc_traceback
+            if filecmp.cmp(file, tempfile):
+                os.remove(tempfile)
+            else:
+                if not trans_filename:
+                    os.rename(tempfile, file)
+                elif type(trans_filename) == type(""):
+                    i = file.rfind(trans_filename[0])
+                    if i > -1:
+                        file = file[:i]
+                    os.rename(tempfile, stem + trans_filename)
+                else:
+                    os.rename(tempfile, trans_filename(file))
+
+def line_by_line(name, infp, outfp, translate_line):
+    "Hook to do line-by-line translation for filters."
+    while 1:
+        line = infp.readline()
+        if line == "":
+            break
+        elif line:	# None returns are skipped
+            outfp.write(translate_line(name, line))
+
+def linefilter(name, arguments, trans_data, trans_filename=None):
+    "Filter framework for line-by-line transformation."
+    return filefilter(name,
+                  arguments,
+                  lambda name, infp, outfp: line_by_line(name, infp, outfp, trans_data),
+                  trans_filename)
+
+def sponge(name, arguments, trans_data, trans_filename=None):
+    "Read input sources entire and transform them in memory."
+    if not arguments:
+        sys.stdout.write(trans_data(name, sys.stdin.read()))
+    else:
+        for file in arguments:
+            infp = open(file)
+            indoc = infp.read()
+            infp.close()
+            tempfile = file + ".~%s-%d~" % (name, os.getpid())
+            try:
+                outfp = open(tempfile, "w")
+            except OSError:
+                sys.stderr.write("%s: can't open tempfile" % name)
+                return 1
+            try:
+                outdoc = trans_data(name, indoc)
+            except:
+                os.remove(tempfile)
+                # Pass the exception upwards
+                (exc_type, exc_value, exc_traceback) = sys.exc_info()
+                raise exc_type, exc_value, exc_traceback
+            if outdoc == indoc:
+                os.remove(tempfile)
+            else:
+                outfp.write(outdoc)
+                if not trans_filename:
+                    os.rename(tempfile, file)
+                elif type(trans_filename) == type(""):
+                    i = file.rfind(trans_filename[0])
+                    if i > -1:
+                        file = file[:i]
+                    os.rename(tempfile, file + trans_filename)
+                else:
+                    os.rename(tempfile, trans_filename(file))
+
+if __name__ == '__main__':
+    import getopt
+
+    def nametrans(name):
+        return name + ".out"
+
+    def filefilter_test(name, infp, outfp):
+        "Test hook for filefilter entry point -- put dashes before blank lines."
+        while 1:
+            line = infp.readline()
+            if not line:
+                break
+            if line == "\n":
+                outfp.write("------------------------------------------\n")
+            outfp.write(line)
+
+    def linefilter_test(name, data):
+        "Test hook for linefilter entry point -- wrap lines in brackets."
+        return "<" + data[:-1] + ">\n"
+
+    def sponge_test(name, data):
+        "Test hook for the sponge entry point -- reverse file lines."
+        lines = data.split("\n")
+        lines.reverse()
+        return "\n".join(lines)
+
+    (options, arguments) = getopt.getopt(sys.argv[1:], "fls")
+    for (switch, val) in options:
+        if switch == '-f':
+            filefilter("filefilter_test", arguments, filefilter_test,nametrans)
+        elif switch == '-l':
+            linefilter("linefilter_test", arguments, linefilter_test,nametrans)
+        elif switch == '-s':
+            sponge("sponge_test", arguments, sponge_test, ".foo")
+        else:
+            print "Unknown option."
+
+# End