I've been reading a lot about closures and I think I understand them, but without clouding the picture for myself and others, I am hoping someone can explain closures as succinctly and clearly as possible. I'm looking for a simple explanation that might help me understand where and why I would want to use them. Closure on closures Objects are data with methods attached, closures are
我一直在阅读很多关于关闭的内容，我想我理解他们，但是没有让我自己和其他人蒙混过关，我希望有人能够尽可能简洁清楚地解释关闭。 我正在寻找一个简单的解释，可以帮助我了解我想要使用它们的位置和原因。 关闭关闭 对象是附带方法的数据，闭包是附带数据的函数。 def make_counter(): i = 0 def counter(): # counter() is a closure nonlocal i i += 1 return i return counter c1
I have JSON data stored in the variable data . I want to write this to a text file for testing so I don't have to grab the data from the server each time. Currently, I am trying this: obj = open('data.txt', 'wb') obj.write(data) obj.close And am receiving the error: TypeError: must be string or buffer, not dict How to fix this? You forgot the actual JSON part - data is a dictionar
我将JSON数据存储在变量data 。 我想写这个文本文件进行测试，所以我不必每次都从服务器获取数据。 目前，我正在尝试这样做： obj = open('data.txt', 'wb') obj.write(data) obj.close 我正在接收错误： TypeError: must be string or buffer, not dict 如何解决这个问题？ 您忘记了实际的JSON部分 - data是字典，尚未JSON编码。 这样写： import json with open('data.txt', 'w') as outfile: json.dump(data
In Python, how can I parse a numeric string like "545.2222" to its corresponding float value, 542.2222 ? Or parse the string "31" to an integer, 31 ? I just want to know how to parse a float string to a float , and (separately) an int string to an int . >>> a = "545.2222" >>> float(a) 545.22220000000004 >>> int(float(a)) 545 def num(s): try:
在Python中，我怎样才能解析一个数字字符串像"545.2222"到它相应的浮点值542.2222 ？ 或者将字符串"31"解析为一个整数31 ？ 我只想知道如何将一个浮点string解析为一个float ，然后（单独）将一个int string解析为一个int 。 >>> a = "545.2222" >>> float(a) 545.22220000000004 >>> int(float(a)) 545 def num(s): try: return int(s) except ValueError:
Let's say you want to save a bunch of files somewhere, for instance in BLOBs. Let's say you want to dish these files out via a web page and have the client automatically open the correct application/viewer. Assumption: The browser figures out which application/viewer to use by the mime-type (content-type?) header in the HTTP response. Based on that assumption, in addition to the byte
假设您想在某处保存一堆文件，例如在BLOB中。 假设您想通过网页提取这些文件，并让客户端自动打开正确的应用程序/查看器。 假设：浏览器找出HTTP响应中mime-type（content-type？）标题使用哪个应用程序/查看器。 基于这种假设，除了文件的字节外，还需要保存MIME类型。 你会如何找到文件的MIME类型？ 我目前在Mac上，但这也应该在Windows上工作。 浏览器在将文件发布到网页时是否添加此信息？ 有没有一个整洁的pyth
What are the lesser-known but useful features of the Python programming language? Try to limit answers to Python core. One feature per answer. Give an example and short description of the feature, not just a link to documentation. Label the feature using a title as the first line. Quick links to answers: Argument Unpacking Braces Chaining Comparison Operators Decorators Defaul
Python编程语言的鲜为人知的但有用的功能是什么？ 尝试限制Python核心的答案。 每个答案一个功能。 给出一个示例和功能的简短描述，而不仅仅是文档的链接。 作为第一行使用标题标记该功能。 快速链接到答案： 参数拆包 背带 链接比较运算符 装饰 默认参数陷阱/可变默认参数的危险 叙 字典默认.get值 文档字符串测试 省略切片语法 列举 对于/其他 函数作为iter（）参数 生成器表达式 import
I want to write a function in Python that returns different fixed values based on the value of an input index. In other languages I would use a switch or case statement, but Python does not appear to have a switch statement. What are the recommended Python solutions in this scenario? 你可以使用字典： def f(x): return { 'a': 1, 'b': 2, }[x] 如果你想使用默认值，你可以使
我想在Python中编写一个函数，它根据输入索引的值返回不同的固定值。 在其他语言中，我会使用switch或case语句，但Python似乎没有switch语句。 在这种情况下推荐的Python解决方案是什么？ 你可以使用字典： def f(x): return { 'a': 1, 'b': 2, }[x] 如果你想使用默认值，你可以使用字典get(key[, default])方法： def f(x): return { 'a': 1, 'b': 2 }.get(x, 9) # 9 is
如何删除Python中的文件或文件夹？ os.remove() will remove a file. os.rmdir() will remove an empty directory. shutil.rmtree() will delete a directory and all its contents. Python Syntax to Delete a file import os os.remove("/tmp/<file_name>.txt") OR import os os.unlink("/tmp/<file_name>.txt") Best Practice: 1. First check whether the file or folder exits or not then only del
如何删除Python中的文件或文件夹？ os.remove()将删除一个文件。 os.rmdir()将删除一个空目录。 shutil.rmtree()将删除一个目录及其所有内容。 Python语法删除文件 import os os.remove("/tmp/<file_name>.txt") 要么 import os os.unlink("/tmp/<file_name>.txt") 最佳实践： 1.首先检查文件或文件夹是否退出，然后只删除该文件。 这可以通过两种方式实现： 一个。 os.path.isfile("/path/to/f
How do you append to the file instead of overwriting it? Is there a special function that appends to the file? with open("test.txt", "a") as myfile: myfile.write("appended text") You need to open the file in append mode, by setting "a" or "ab" as the mode. See open(). When you open with "a" mode, the write position will always be at the end of the file (an
你如何附加到文件而不是覆盖它？ 有附加到文件的特殊功能吗？ with open("test.txt", "a") as myfile: myfile.write("appended text") 您需要以附加模式打开文件，方法是将“a”或“ab”设置为模式。 参见open（）。 当以“a”模式打开时，写入位置将始终位于文件的末尾（追加）。 您可以用“a +”打开以允许读取，反向查找和读取（但所有写入仍将在文件末尾！）。 例： >>> with open('test1','wb') as f:
How do I read every line of a file in Python and store each line as an element in a list? I want to read the file line by line and append each line to the end of the list. with open(fname) as f: content = f.readlines() # you may also want to remove whitespace characters like `n` at the end of each line content = [x.strip() for x in content] 我猜你的意思是list而不是数组。 See Input and Ou
如何在Python中读取文件的每一行并将每行存储为列表中的元素？ 我想逐行读取文件，并将每行添加到列表的末尾。 with open(fname) as f: content = f.readlines() # you may also want to remove whitespace characters like `n` at the end of each line content = [x.strip() for x in content] 我猜你的意思是list而不是数组。 请参阅输入和输出： with open('filename') as f: lines = f.readlines() 或剥离换
How do I copy a file in Python? I couldn't find anything under os . shutil has many methods you can use. One of which is: from shutil import copyfile copyfile(src, dst) Copy the contents of the file named src to a file named dst . The destination location must be writable; otherwise, an IOError exception will be raised. If dst already exists, it will be replaced. Special files such
如何在Python中复制文件？ 我在os下找不到任何东西。 shutil有很多方法可以使用。 其中之一是： from shutil import copyfile copyfile(src, dst) 将名为src的文件的内容复制到名为dst的文件中。 目标位置必须可写; 否则，会IOError异常。 如果dst已经存在，它将被替换。 特殊文件如字符或块设备和管道不能使用此功能进行复制。 src和dst是以字符串形式给出的路径名。 copy2(src,dst)通常比copyfile(src,dst)更有