Python 检查文件是否存在但实际文件确实存在

Question

我正在用Flask写一个应用程序，某个时候我想启动一个快速的进程，然后检查服务器上是否有输出。如果有输出，就下载它；如果没有，就显示相应的提示信息。

这是我的代码：

import os
import subprocess
import sqlite3
from flask import Flask, render_template, request, redirect, g, send_from_directory

app = Flask(__name__)
app.config.from_object(__name__)

# Config
app.config.update(dict(
    DATABASE = os.path.join(app.root_path, 'database/records.db'),
    DEBUG = True,
    UPLOAD_FOLDER = 'uploads',
    OUTPUT_FOLDER = 'outputs',
    ALLOWED_EXTENSIONS = set(['txt', 'gro', 'doc', 'docx'])
    ))

def allowed_file(filename):
    return '.' in filename and \
           filename.rsplit('.', 1)[1] in app.config['ALLOWED_EXTENSIONS']

def run_calculations(filename):
    subprocess.call(['python', os.path.join(app.root_path, 'topologia.py'), 'uploads/' + filename])

def get_db():
    db = getattr(g, '_database', None)
    if db is None:
        db = g._database = sqlite3.connect(app.config['DATABASE'])
    return db

@app.teardown_appcontext
def close_connection(exception):
    db = getattr(g, '_database', None)
    if db is not None:
        db.close()

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/outputs/<filename>')
def calculated_record(filename):
    return send_from_directory(app.config['OUTPUT_FOLDER'], filename)

@app.route('/upload', methods = ['GET', 'POST'])
def upload():
    with app.app_context():
        cur = get_db().cursor()
        cur.execute('INSERT INTO records(calculated) VALUES(0)')
        file_id = cur.lastrowid
        get_db().commit()
    file = request.files['file']
    if file and allowed_file(file.filename):
        input_file = str(file_id) +'.'+file.filename.rsplit('.', 1)[1]
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], input_file))
        run_calculations(input_file)
        output_name = '/outputs/topologia_wynik' + str(file_id) + '.top'
        if os.path.isfile(output_name):
            return redirect(output_name)
        else:
            return 'Your file is beeing loaded'
    else:
        return "Something went wrong, check if your file is in right format ('txt', 'gro', 'doc', 'docx')"


if __name__ == '__main__':
    app.run()

我整个问题出在这段代码上：

            if os.path.isfile(output_name):
                return redirect(output_name)
            else:
                return 'Your file is beeing loaded'

因为这个条件永远不成立……当我删除这部分代码，直接跳转到输出文件而不检查时，一切都正常……你知道这是为什么吗？

应用程序开发进程管理文件检查错误调试 flask 服务器输出

Python 检查文件是否存在但实际文件确实存在

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