如何在python中的另一个函数创建文本文件之前读取该文件

Question

在我的python代码中，我调用了一个用FreeFem++编写的函数，然后将FreeFem++代码的输出保存在一个文本文件中，我想在python中读取它。

def f(x):
    os.system("Here the FreeFem++ code will be called and the result will be saved as out.txt")
    myfile=open("out.txt")
    return myfile.read()

问题是，当我运行python代码时，由于还没有创建out.txt，它会给我一个错误，告诉我out.txt不存在！

Answer 1

使用subprocess.run()调用您的freefem++程序，并确保您的调用在文件存在之前实际生成了该文件。您可以通过在open之前添加断点来检查这一点。

因此，更改为subprocess：

def f(x):
    cp = subprocess.run(['freefem++', '--argument', '--other_argument'])
    if cp.returncode != 0:
        print('Oops… failure running freefem++!')
        sys.exit(cp.returncode) # actually you should be raising an exception as you're in a function
    if not os.path.exists('out.txt'):
        print('Oops… freefem++ failed to create the file!')
        sys.exit(1) # same you'd better be raising an exception as you're in a function
    with open('out.txt', 'r') as ff_out:
        return ff_out # it is better to return the file object so you can iterate over it

要在打开文件之前检查文件是否已创建，请执行以下操作：

def f(x):
    cp = subprocess.run(['freefem++', '--argument', '--other_argument'])
    if cp.returncode != 0:
        print('Oops… failure running freefem++!')
        sys.exit(cp.returncode)

    # XXX Here we make a breakpoint, when it's stopping open a shell and check for the file!
    # if you do not find the file at this point, then your freefem++ call is buggy and your issue is not in the python code, but in the freefem++ code.
    import pdb;pdb.set_trace()

    with open('out.txt', 'r') as ff_out:
        return ff_out # it is better to return the file object so you can iterate over it

最后，对于您来说，最好的解决方案是让freefem++程序将所有内容输出到标准输出，然后使用subprocess.popen()通过python中的管道获取输出

def f(x):
    p = subprocess.popen(['freefem++'…], stdout=subprocess.PIPE)
    out, _ = p.communicate()
    if p.returncode != 0:
        raise Exception('Oops, freefem++ failed!')
    return out