在循环中，可选地将输出写入文件

Question

我编写了一个迭代性计算一些数量x，y的函数，以返回最终结果。此外，此代码将x，y的每次迭代保存到文件中。这是基本结构：

def myFunc():
    X,Y = 0,0
    file1 = open(output1,"w")
    file2 = open(output2,"w")
    for i in range(1000):
        X,Y = someCalculation(X,Y) #calculations happen here
        file1.write(X)
        file2.write(Y)
    file1.close()
    file2.close()
    return X,Y

但是，如果文件名 或output2在调用函数时省略了，我需要此函数才能执行相同的计算而无需附加相关文件的任何内容。

这是我凌乱的解决方案：

def myFunc(output1=None,output2=None):
    X,Y = 0,0
    if (output1 != None): file1 = open(output1,"w")
    if (output2 != None): file2 = open(output2,"w")
    for i in range(1000):
        X,Y = someCalculation(X,Y) #calculations happen here
        if (output1 != None): file1.write(X)
        if (output2 != None): file2.write(Y)
    if (output1 != None): file1.close()
    if (output2 != None): file2.close()
    return X,Y

是否有一种更好，更干净的写作方式？

Answer 1

制作一个虚拟文件对象，忽略写入并支持上下文管理器接口：

class NoFile:
    def __enter__(self): return self
    # Propagate any exceptions that were raised, explicitly.
    def __exit__(self, exc_type, exc_value, exc_tb): return False
    # Ignore the .write method when it is called.
    def write(self, data): pass
    # We can extend this with other dummy behaviours, e.g.
    # returning an empty string if there is an attempt to read.

创建一个辅助函数，当文件名 none 时，创建其中一个而不是普通文件：

def my_open(filename, *args, **kwargs):
    return NoFile() if filename is None else open(filename, *args, **kwargs)

使用代码>块来管理文件寿命，就像您应该做的那样 - 但是现在使用my_open而不是open：

def myFunc(output1=None,output2=None):
    X, Y = 0, 0
    with my_open(output1, 'w') as f1, my_open(output2, 'w') as f2:
        for i in range(1000):
            X, Y = someCalculation(X, Y) #calculations happen here
            f1.write(X)
            f2.write(Y)
    return X, Y

Answer 2

您可以创建一个虚拟类，该类没有do <代码>写方法。 ExitStack用于确保自动关闭任何打开的文件。

from contextlib import ExitStack


class NoWrite:
    def write(self, value):
        pass


def myFunc(output1=None, output2=None):
    X,Y = 0,0
    with ExitStack() as es:
        file1 = es.enter_context(open(output1, "w")) if output1 is not None else NoWrite()
        file2 = es.enter_context(open(output2, "w")) if output2 is not None else NoWrite()

        for i in range(1000):
            X,Y = someCalculation(X, Y) #calculations happen here
            file1.write(X)
            file2.write(Y)
    return X,Y

---

当您似乎正在记录x和/或y值时，您可能需要考虑使用logging模块，为适当的记录器创建fileHandler，而不是将输出文件名称为myFunc本身。

import logging

# configuration of the logger objects is the responsibility
# of the *user* of the function, not the function itself.
def myFunc():
    x_logger = logging.getLogger("myFunc.x_logger")
    y_logger = logging.getLogger("myFunc.y_logger")

    X,Y = 0,0
    for i in range(1000):
        X,Y = someCalculation(X, Y)
        x_logger.info("%s", X)
        y_logger.info("%s", Y)
    return X,Y

Answer 3

简单：写入操作系统定义的“空设备”文件，以免写信给。

标准库OS模块定义字符串常数devNull，它标识了此文件的路径：'/dev/null' Mac and Linux上'nul'在Windows上（我想后者实际上不是路径）。

import os
def myFunc(output1=os.devnull,output2=os.devnull):
    # as before, with no special conditional logic