如何与 python 中的 EXE 交互？

Question

I'm doing some work that need to call an EXE with c++ in Python. Take an example, I want to interact with below program to get the output message and enter the necessary input in Python.

    #include <iostream>
    #include <cmath>
    using namespace std;
    int main()
    {
        double init_asset;  // the money you have at the beginning
        double ratio;       // the gain ratio you will get after every year
        double years;       // how many years you want to wait
        double future_gain;
        cout << "Please tell me how much money you want to invest now:\n";
        fflush(stdout);
        cin >> init_asset;
        cout << "Please tell me the gain ratio you will have after each year:\n";
        fflush(stdout);
        cin >> ratio;
        cout << "Please tell me how many years you want to wait:\n";
        fflush(stdout);
        cin >> years; 
        future_gain = init_asset*pow((1+ratio),years);
        cout << "Your future gain is: " << future_gain << " after " << years << " years.\n";
        fflush(stdout);
        return 0;
    } 

In Python, I tried below code:

p1 = subprocess.Popen(["./calc_return"],stdin=subprocess.PIPE, stdout=subprocess.PIPE)
for line in iter(p1.stdout.readline, b''):
    print(line)
    info = input("Please enter info based on the above request:")
    out, err = p1.communicate(bytes(info,'utf-8'))
    print(out)

But the code doesn't work, the communication function terminates the calc_return program and the
code stuck in the for loops.

Can anyone help me out this question? Thanks in advance.

Answer 1

You can create a wrapper in Python to get all the parameters and then call the Exe with just one line.

os.system("program.exe {} {}".format(param1, param2))

Ref: https://stackabuse.com/executing-shell-commands-with-python/

Answer 2

Well communicate name confused you... It does not manage a true 2 channel communication but rather:

1. pass an initial input to the command
2. wait for the command to terminate with no other interaction
3. give back the stout and stderr output to the caller.

And it is not what you want.

You must instead simply read the stdout channel without waiting for the command to terminate and pass the user input to the stdin channel of the command.

You code could become:

p1 = subprocess.Popen(["./calc_return"],stdin=subprocess.PIPE, stdout=subprocess.PIPE)
for line in iter(p1.stdout, b''):   # do not use readline here...
    print(line)
    if p1.poll() is not None:  # exit loop if the command completed
        break
    info = input("Please enter info based on the above request:")
    print(info, file=p1.stdin)

But beware:

• this will only work because the program consistently flushes its output before inputting anything
• this code has a minor race condition: nothing can guarantee that the command will be ended before you reach p1.poll() . A possible workaround is to just warn your users that if the message is not a question they can provide any input.

Unfortunately that last point is not easy to cope with. It would require multithreading to have one thread processing the input channel while the other processes the output channel. It would be overkill here but cannot be avoided in a portable way for more serious use cases.