# `filecmp` --- 檔案與目錄比較

原始碼： Lib/filecmp.py

The `filecmp` module defines functions to compare files and directories, with various optional time/correctness trade-offs. For comparing files, see also the `difflib` module.

The `filecmp` module defines the following functions:

filecmp.cmp(f1, f2, shallow=True)

  Compare the files named f1 and f2, returning `True` if they seem equal, `False` otherwise.

  If shallow is true and the `os.stat()` signatures (file type, size, and modification time) of both files are identical, the files are taken to be equal.

  Otherwise, the files are treated as different if their sizes or contents differ.

  Note that no external programs are called from this function, giving it portability and efficiency.

  This function uses a cache for past comparisons and the results, with cache entries invalidated if the `os.stat()` information for the file changes. The entire cache may be cleared using `clear_cache()`.

filecmp.cmpfiles(dir1, dir2, common, shallow=True)

  Compare the files in the two directories dir1 and dir2 whose names are given by common.

  Returns three lists of file names: match, mismatch, errors. match contains the list of files that match, mismatch contains the names of those that don't, and errors lists the names of files which could not be compared. Files are listed in errors if they don't exist in one of the directories, the user lacks permission to read them or if the comparison could not be done for some other reason.

  The shallow parameter has the same meaning and default value as for `filecmp.cmp()`.

  For example, `cmpfiles('a', 'b', ['c', 'd/e'])` will compare `a/c` with `b/c` and `a/d/e` with `b/d/e`. `'c'` and `'d/e'` will each be in one of the three returned lists.

filecmp.clear_cache()

  Clear the filecmp cache. This may be useful if a file is compared so quickly after it is modified that it is within the mtime resolution of the underlying filesystem.

  在 3.4 版被加入.

## The `dircmp` class

class filecmp.dircmp(a, b, ignore=None, hide=None)

  Construct a new directory comparison object, to compare the directories a and b. ignore is a list of names to ignore, and defaults to `filecmp.DEFAULT_IGNORES`. hide is a list of names to hide, and defaults to `[os.curdir, os.pardir]`.

  The `dircmp` class compares files by doing shallow comparisons as described for `filecmp.cmp()`.

  The `dircmp` class provides the following methods:

  report()

    Print (to `sys.stdout`) a comparison between a and b.

  report_partial_closure()

    Print a comparison between a and b and common immediate subdirectories.

  report_full_closure()

    Print a comparison between a and b and common subdirectories (recursively).

  The `dircmp` class offers a number of interesting attributes that may be used to get various bits of information about the directory trees being compared.

  Note that via `__getattr__()` hooks, all attributes are computed lazily, so there is no speed penalty if only those attributes which are lightweight to compute are used.

  left

    The directory a.

  right

    The directory b.

  left_list

    Files and subdirectories in a, filtered by hide and ignore.

  right_list

    Files and subdirectories in b, filtered by hide and ignore.

  common

    Files and subdirectories in both a and b.

  left_only

    Files and subdirectories only in a.

  right_only

    Files and subdirectories only in b.

  common_dirs

    Subdirectories in both a and b.

  common_files

    Files in both a and b.

  common_funny

    Names in both a and b, such that the type differs between the directories, or names for which `os.stat()` reports an error.

  same_files

    Files which are identical in both a and b, using the class's file comparison operator.

  diff_files

    Files which are in both a and b, whose contents differ according to the class's file comparison operator.

  funny_files

    Files which are in both a and b, but could not be compared.

  subdirs

    A dictionary mapping names in `common_dirs` to `dircmp` instances (or MyDirCmp instances if this instance is of type MyDirCmp, a subclass of `dircmp`).

    在 3.10 版的變更: Previously entries were always `dircmp` instances. Now entries are the same type as self, if self is a subclass of `dircmp`.

filecmp.DEFAULT_IGNORES

  在 3.4 版被加入.

  List of directories ignored by `dircmp` by default.

Here is a simplified example of using the `subdirs` attribute to search recursively through two directories to show common different files:

    >>> from filecmp import dircmp
    >>> def print_diff_files(dcmp):
    ...     for name in dcmp.diff_files:
    ...         print("diff_file %s found in %s and %s" % (name, dcmp.left,
    ...               dcmp.right))
    ...     for sub_dcmp in dcmp.subdirs.values():
    ...         print_diff_files(sub_dcmp)
    ...
    >>> dcmp = dircmp('dir1', 'dir2')
    >>> print_diff_files(dcmp)