python知识点:tkinter-filedialog-asksaveasfilename参数
# For the following classes and modules:
#
# options (all have default values):
#
# - defaultextension: added to filename if not explicitly given
#
# - filetypes: sequence of (label, pattern) tuples. the same pattern
# may occur with several patterns. use "*" as pattern to indicate
# all files.
#
# - initialdir: initial directory. preserved by dialog instance.
#
# - initialfile: initial file (ignored by the open dialog). preserved
# by dialog instance.
#
# - parent: which window to place the dialog on top of
#
# - title: dialog title
#
# - multiple: if true user may select more than one file
#
# options for the directory chooser:
#
# - initialdir, parent, title: see above
#
# - mustexist: if true, user must pick an existing directory
#