python:检查文件是否存在，如果不存在，则创建它

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我试了一试:接住，但不管用。我想我可以把它改成if语句，但是不明白为什么这个不行。这是我第一个"真正"的项目。我正在构建一个灌溉控制器，并创建一个灌溉时间表字典。第一个代码是我目前拥有的代码，第二个代码是我正在尝试的"测试"本身。每当我运行代码时，它都会重写现有文件，而我想让它打开文件(如果文件已经存在)，然后不再重写它。

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# timer will first look for a saved file(dictionary) of already recorded
# irrigation times. If no file exists it will create one.

# irrigation timer which does scheduled irrigation as well as cyclic irrigation for propagating plants.
# uses a lcd 1602 display
# will use up to 10 different valves

import time
import datetime
import threading
import RPi.GPIO as GPIO
from RPLCD import CharLCD # http://www.circuitbasics.com/raspberry-pi-lcd-set-up-and-programming-in-python/

GPIO.setmode(GPIO.BOARD)

# pinouts for lcd pins
lcd = CharLCD (cols=16, rows=2, pin_rs=37, pin_e=35, pins_data=[33, 31, 29, 23])

# valve pins
valve_1 = 8
valve_2 = 10
valve_3 = 12
valve_4 = 16
valve_5 = 18
valve_6 = 22
valve_7 = 24
valve_8 = 26
valve_9 = 32
valve_10 = 36

# setup valve pins as outputs
GPIO.setup(valve_pin1, GPIO.OUT)
GPIO.setup(valve_pin2, GPIO.OUT)
GPIO.setup(valve_pin3, GPIO.OUT)
GPIO.setup(valve_pin4, GPIO.OUT)
GPIO.setup(valve_pin5, GPIO.OUT)
GPIO.setup(valve_pin6, GPIO.OUT)
GPIO.setup(valve_pin7, GPIO.OUT)
GPIO.setup(valve_pin8, GPIO.OUT)
GPIO.setup(valve_pin9, GPIO.OUT)
GPIO.setup(valve_pin10, GPIO.OUT)

#set all valve pins to off
GPIO.output(valve_pin1, False)
GPIO.output(valve_pin2, False)
GPIO.output(valve_pin3, False)
GPIO.output(valve_pin4, False)
GPIO.output(valve_pin5, False)
GPIO.output(valve_pin6, False)
GPIO.output(valve_pin7, False)
GPIO.output(valve_pin8, False)
GPIO.output(valve_pin9, False)
GPIO.output(valve_pin10, False)

# check to see if a schedule has been saved
def sched_check()
try:
file = open("schedule.dat","r")
schedule = schedule.read()
file.close()
# create a list of schedule dictionaries
except:
schedule_list = []
for schedule_number in range(10):
schedule = {
"timed" : {
"watering_days" : [],
"watering_times" : [],
"duration" :"timed_duration",
},
"cyclic" : {
"time_on" :"seconds_on",
"time_off" :"seconds_off",
"blackout_window_start" :"blkout_time_start",
"blackout_window_stop" :"blkout_time_stop",
},
}
schedule_list.append(schedule)
file = open("schedule.dat","w")
file.write(str(schedule_list))
file.close()

这就是问题所在。

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def sched_check():
try:
file = open("schedule.dat","r")
schedule = schedule.read()
file.close()
print("file already exists")
# create a list of schedule dictionaries
except:
schedule_list = []
for schedule_number in range(10):
schedule = {
"timed" : {
"watering_days" : [],
"watering_times" : [],
"duration" :"timed_duration",
},
"cyclic" : {
"time_on" :"seconds_on",
"time_off" :"seconds_off",
"blackout_window_start" :"blkout_time_start",
"blackout_window_stop" :"blkout_time_stop",
},
}
schedule_list.append(schedule)
file = open("schedule.dat","w")
file.write(str(schedule_list))
file.close()
print("new file created")

sched_check()