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tools/misc_utils.py

Index: tools/misc_utils.py
diff --git a/tools/misc_utils.py b/tools/misc_utils.py
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+++ b/tools/misc_utils.py
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+# Copyright 2014 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+
+"""Module to host the VerboseSubprocess, ChangeDir, and ReSearch classes.
+"""
+
+import os
+import re
+import subprocess
+
+
+def print_subprocess_args(prefix, *args, **kwargs):
+    """Print out args in a human-readable manner."""
+    def quote_and_escape(string):
+        """Quote and escape a string if necessary."""
+        if ' ' in string or '\n' in string:
+            string = '"%s"' % string.replace('"', '\\"')
+        return string
+    if 'cwd' in kwargs:
+        print '%scd %s' % (prefix, kwargs['cwd'])
+    print prefix + ' '.join(quote_and_escape(arg) for arg in args[0])
+    if 'cwd' in kwargs:
+        print '%scd -' % prefix
+
+
+class VerboseSubprocess(object):
+    """Call subprocess methods, but print out command before executing.
+
+    Attributes:
+        verbose: (boolean) should we print out the command or not.  If
+                 not, this is the same as calling the subprocess method
+        quiet: (boolean) suppress stdout on check_call and call.
+        prefix: (string) When verbose, what to print before each command.
+    """
+
+    def __init__(self, verbose):
+        self.verbose = verbose
+        self.quiet = not verbose
+        self.prefix = '~~$ '
+
+    def check_call(self, *args, **kwargs):
+        """Wrapper for subprocess.check_call().
+
+        Args:
+            *args: to be passed to subprocess.check_call()
+            **kwargs: to be passed to subprocess.check_call()
+        Returns:
+            Whatever subprocess.check_call() returns.
+        Raises:
+            OSError or subprocess.CalledProcessError: raised by check_call.
+        """
+        if self.verbose:
+            print_subprocess_args(self.prefix, *args, **kwargs)
+        if self.quiet:
+            with open(os.devnull, 'w') as devnull:
+                return subprocess.check_call(*args, stdout=devnull, **kwargs)
+        else:
+            return subprocess.check_call(*args, **kwargs)
+
+    def call(self, *args, **kwargs):
+        """Wrapper for subprocess.check().
+
+        Args:
+            *args: to be passed to subprocess.check_call()
+            **kwargs: to be passed to subprocess.check_call()
+        Returns:
+            Whatever subprocess.call() returns.
+        Raises:
+            OSError or subprocess.CalledProcessError: raised by call.
+        """
+        if self.verbose:
+            print_subprocess_args(self.prefix, *args, **kwargs)
+        if self.quiet:
+            with open(os.devnull, 'w') as devnull:
+                return subprocess.call(*args, stdout=devnull, **kwargs)
+        else:
+            return subprocess.call(*args, **kwargs)
+
+    def check_output(self, *args, **kwargs):
+        """Wrapper for subprocess.check_output().
+
+        Args:
+            *args: to be passed to subprocess.check_output()
+            **kwargs: to be passed to subprocess.check_output()
+        Returns:
+            Whatever subprocess.check_output() returns.
+        Raises:
+            OSError or subprocess.CalledProcessError: raised by check_output.
+        """
+        if self.verbose:
+            print_subprocess_args(self.prefix, *args, **kwargs)
+        return subprocess.check_output(*args, **kwargs)
+
+    def strip_output(self, *args, **kwargs):
+        """Wrap subprocess.check_output and str.strip().
+
+        Pass the given arguments into subprocess.check_output() and return
+        the results, after stripping any excess whitespace.
+
+        Args:
+            *args: to be passed to subprocess.check_output()
+            **kwargs: to be passed to subprocess.check_output()
+
+        Returns:
+            The output of the process as a string without leading or
+            trailing whitespace.
+        Raises:
+            OSError or subprocess.CalledProcessError: raised by check_output.
+        """
+        if self.verbose:
+            print_subprocess_args(self.prefix, *args, **kwargs)
+        return str(subprocess.check_output(*args, **kwargs)).strip()
+
+    def popen(self, *args, **kwargs):
+        """Wrapper for subprocess.Popen().
+
+        Args:
+            *args: to be passed to subprocess.Popen()
+            **kwargs: to be passed to subprocess.Popen()
+        Returns:
+            The output of subprocess.Popen()
+        Raises:
+            OSError or subprocess.CalledProcessError: raised by Popen.
+        """
+        if self.verbose:
+            print_subprocess_args(self.prefix, *args, **kwargs)
+        return subprocess.Popen(*args, **kwargs)
+
+
+class ChangeDir(object):
+    """Use with a with-statement to temporarily change directories."""
+    # pylint: disable=I0011,R0903
+
+    def __init__(self, directory, verbose=False):
+        self._directory = directory
+        self._verbose = verbose
+
+    def __enter__(self):
+        if self._directory != os.curdir:
+            if self._verbose:
+                print '~~$ cd %s' % self._directory
+            cwd = os.getcwd()
+            os.chdir(self._directory)
+            self._directory = cwd
+
+    def __exit__(self, etype, value, traceback):
+        if self._directory != os.curdir:
+            if self._verbose:
+                print '~~$ cd %s' % self._directory
+            os.chdir(self._directory)
+
+
+class ReSearch(object):
+    """A collection of static methods for regexing things."""
+
+    @staticmethod
+    def search_within_stream(input_stream, pattern, default=None):
+        """Search for regular expression in a file-like object.
+
+        Opens a file for reading and searches line by line for a match to
+        the regex and returns the parenthesized group named return for the
+        first match.  Does not search across newlines.
+
+        For example:
+            pattern = '^root(:[^:]*){4}:(?P<return>[^:]*)'
+            with open('/etc/passwd', 'r') as stream:
+                return search_within_file(stream, pattern)
+        should return root's home directory (/root on my system).
+
+        Args:
+            input_stream: file-like object to be read
+            pattern: (string) to be passed to re.compile
+            default: what to return if no match
+
+        Returns:
+            A string or whatever default is
+        """
+        pattern_object = re.compile(pattern)
+        for line in input_stream:
+            match = pattern_object.search(line)
+            if match:
+                return match.group('return')
+        return default
+
+    @staticmethod
+    def search_within_string(input_string, pattern, default=None):
+        """Search for regular expression in a string.
+
+        Args:
+            input_string: (string) to be searched
+            pattern: (string) to be passed to re.compile
+            default: what to return if no match
+
+        Returns:
+            A string or whatever default is
+        """
+        match = re.search(pattern, input_string)
+        return match.group('return') if match else default
+
+    @staticmethod
+    def search_within_output(verbose, pattern, default, *args, **kwargs):
+        """Search for regular expression in a process output.
+
+        Does not search across newlines.
+
+        Args:
+            verbose: (boolean) shoule we call print_subprocess_args?
+            pattern: (string) to be passed to re.compile
+            default: what to return if no match
+            *args: to be passed to subprocess.Popen()
+            **kwargs: to be passed to subprocess.Popen()
+
+        Returns:
+            A string or whatever default is
+        """
+        if verbose:
+            print_subprocess_args('~~$ ', *args, **kwargs)
+        proc = subprocess.Popen(*args, stdout=subprocess.PIPE, **kwargs)
+        return ReSearch.search_within_stream(proc.stdout, pattern, default)
+
+