python创建型设计模式——建造者模式

建造者模式

与工厂模式相似，用于创建需要由多个对象组成的复杂对象。区别在于他不仅提供了创建复杂对象所需要的方法，而且保存了复杂对象里的各个部分的细节。适用于需要把复杂对象各个部分的细节与其创建流程相分离的场合。

表单生成程序的例子，分别生成HTML和ThinkerGUI表单

建造者模式案例

最顶层调用

创建两个表单，并分别写入对应文件中，都会调用create_login_form()并传入建造者对象

def main():
    if len(sys.argv) > 1 and sys.argv[1] == "-P": # For regression testing
        print(create_login_form(HtmlFormBuilder()))
        print(create_login_form(TkFormBuilder()))
        return

    htmlFilename = os.path.join(tempfile.gettempdir(), "login.html")
    htmlForm = create_login_form(HtmlFormBuilder())
    with open(htmlFilename, "w", encoding="utf-8") as file:
        file.write(htmlForm)
    print("wrote", htmlFilename)

    tkFilename = os.path.join(tempfile.gettempdir(), "login.py")
    tkForm = create_login_form(TkFormBuilder())
    with open(tkFilename, "w", encoding="utf-8") as file:
        file.write(tkForm)
    print("wrote", tkFilename)

create_login_form()函数

调用builder的设置方法，然后由builder拼接对象，返回复杂的对象。与工厂模式的却别在于，工厂模式这里是直接由工厂创建相关简单对象以及复杂对象，复杂对象调用自己的方法进行拼接，然后返回自己

def create_login_form(builder):
    builder.add_title("Login")
    builder.add_label("Username", 0, 0, target="username")
    builder.add_entry("username", 0, 1)
    builder.add_label("Password", 1, 0, target="password")
    builder.add_entry("password", 1, 1, kind="password")
    builder.add_button("Login", 2, 0)
    builder.add_button("Cancel", 2, 1)
    return builder.form()

建造者类

HtmlFormBuilder类

表单中的控件保存在items字典中，字典的键是row与column构成的二元组，值为控件html代码

class HtmlFormBuilder(AbstractFormBuilder):

    def __init__(self):
        self.title = "HtmlFormBuilder"
        self.items = {}

    def add_title(self, title):
        super().add_title(escape(title))

    def add_label(self, text, row, column, **kwargs):
        self.items[(row, column)] = ('<td><label for="{}">{}:</label></td>'
                .format(kwargs["target"], escape(text)))

    def add_entry(self, variable, row, column, **kwargs):
        html = """<td><input name="{}" type="{}" /></td>""".format(
                variable, kwargs.get("kind", "text"))
        self.items[(row, column)] = html

    def add_button(self, text, row, column, **kwargs):
        html = """<td><input type="submit" value="{}" /></td>""".format(
                escape(text))
        self.items[(row, column)] = html

    def form(self):
        html = ["<!doctype html>\n<html><head><title>{}</title></head>"
                "<body>".format(self.title), '<form><table border="0">']
        thisRow = None
        for key, value in sorted(self.items.items()):
            row, column = key
            if thisRow is None:
                html.append("  <tr>")
            elif thisRow != row:
                html.append("  </tr>\n  <tr>")
            thisRow = row
            html.append("    " + value)
        html.append("  </tr>\n</table></form></body></html>")
        return "\n".join(html)

TkFormBuilder类

由statement字典来存放组件创建和设置的语句，有extends()函数来扩充该字典。_canonicalize()用于格式化处理字符串，设置在数字开头的字符串前增加 “_”，并且可以根据需要，设置首字母大小写

class TkFormBuilder(AbstractFormBuilder):

    TEMPLATE = """#!/usr/bin/env python3
import tkinter as tk
import tkinter.ttk as ttk

class {name}Form(tk.Toplevel):

    def __init__(self, master):
        super().__init__(master)
        self.withdraw()     # hide until ready to show
        self.title("{title}")
        {statements}
        self.bind("<Escape>", lambda *args: self.destroy())
        self.deiconify()    # show when widgets are created and laid out
        if self.winfo_viewable():
            self.transient(master)
        self.wait_visibility()
        self.grab_set()
        self.wait_window(self)

if __name__ == "__main__":
    application = tk.Tk()
    window = {name}Form(application)
    application.protocol("WM_DELETE_WINDOW", application.quit)
    application.mainloop()
"""

    def __init__(self):
        self.title = "TkFormBuilder"
        self.statements = []

    def add_title(self, title):
        super().add_title(title)

    def add_label(self, text, row, column, **kwargs):
        name = self._canonicalize(text)
        create = """self.{}Label = ttk.Label(self, text="{}:")""".format(
                name, text)
        layout = """self.{}Label.grid(row={}, column={}, sticky=tk.W, \
padx="0.75m", pady="0.75m")""".format(name, row, column)
        self.statements.extend((create, layout))

    def add_entry(self, variable, row, column, **kwargs):
        name = self._canonicalize(variable)
        extra = "" if kwargs.get("kind") != "password" else ', show="*"'
        create = "self.{}Entry = ttk.Entry(self{})".format(name, extra)
        layout = """self.{}Entry.grid(row={}, column={}, sticky=(\
tk.W, tk.E), padx="0.75m", pady="0.75m")""".format(name, row, column)
        self.statements.extend((create, layout))

    def add_button(self, text, row, column, **kwargs):
        name = self._canonicalize(text)
        create = ("""self.{}Button = ttk.Button(self, text="{}")"""
                .format(name, text))
        layout = """self.{}Button.grid(row={}, column={}, padx="0.75m", \
pady="0.75m")""".format(name, row, column)
        self.statements.extend((create, layout))

    def form(self):
        return TkFormBuilder.TEMPLATE.format(title=self.title,
                name=self._canonicalize(self.title, False),
                statements="\n        ".join(self.statements))

    def _canonicalize(self, text, startLower=True):
        text = re.sub(r"\W+", "", text)
        if text[0].isdigit():
            return "_" + text
        return text if not startLower else text[0].lower() + text[1:]

补充知识点

python tempfile 模块
http://blog.csdn.net/liangzhao_jay/article/details/17719953

python继承的实现：
基类设置mateclass参数为abc模块中的ABCMeta,并用 @abc.abstractmethod装饰器装饰抽象方法。如果这么设置，则该类将无法初始化，但是会增加运行期开销，一般采用更为宽松的做法，不用mateclass，而是直接在文档中说明，该类是抽象基类。

class AbstractFormBuilder(metaclass=abc.ABCMeta):

    @abc.abstractmethod
    def add_title(self, title):
        self.title = title


    @abc.abstractmethod
    def form(self):
        pass


    @abc.abstractmethod
    def add_label(self, text, row, column, **kwargs):
        pass


    @abc.abstractmethod
    def add_entry(self, variable, row, column, **kwargs):
        pass


    @abc.abstractmethod
    def add_button(self, text, row, column, **kwargs):
        pass

序列与映射的解包操作：