Python 删除现有文件的内容并重新写入内容

专家们，这是一个常见的问题，我尝试了基于SO中的解决方案和示例，但仍然存在将所有设备的打印输出写入文件的问题。我使用了几种方法进行测试，大多数时候我只得到文本文件中的最后一行输出。 下面的问题和我的差不多，但我运气不好

我测试脚本以根据设备类型运行特定命令。如果设备A运行命令A，如果设备B运行命令B，如果设备C运行命令C。文本文件中的设备列表（该列表具有类型和ip地址）。当我使用“w”时，文件内容仅在最后一行，但当我使用“a”时，它将保存列表中所有设备的所有内容，但当我再次运行脚本时，它将继续在最后一个指针上写入，因此我得到了重复的内容..它追加并保持追加

当使用outFileName时，“w” 输出内容仅取最后一行内容

OUTPUT CONTENT for device type C IP 10.2.10.12

当使用outFileName时，“a” 第一次运行脚本时输出内容，如下所示

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12
OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

#Define functions for each device_type
def type_A(ip):
    return{
        'device_type': 'A',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

def type_B(ip):
    return{
        'device_type': 'B',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

def type_C(ip):
    return{
        'device_type': 'C',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

#Function to create output text file
def writeOutFile(outFileName, string):
    with open(outFileName, "w") as f:
       outfile = f.write(string)

#Open Text file that contain device type and ip address
deviceFile = open('devices.txt','r')

#Create list llist for each line in the file.  
#The first item is the device type, 
#The second item is the IP address
for line in deviceFile:
    llist = line.split()
    ipAd = llist[1]

    #Check the first item of the list to determine device type and set 
    #variables
    if llist[0] == 'A':
        dvs = type_A(ipAd)
        sendCommand = 'command for device type A'
    elif llist[0] == 'B':
        dvs = type_B(ipAd)
        sendCommand = 'command for device type B'
    elif llist[0] == 'C':
        dvs = type_C(ipAd)
        sendCommand = 'command for device type c'
    else:
        print("no valid device type")
        break

    dvs_connect = ConnectHandler(**dvs)
    sendCommand = (dvs_connect.send_command(sendCommand))
    #This print all the devices output on the terminal
    print(sendCommand)

    #Generate output file
    outFileName = "outputFile.txt"

    #function call to write the output string into a text file
    writeOutFile(outFileName, sendCommand)

    dvs_connect.disconnect()

deviceFile.close()

第二次运行脚本时…该文件包含重复项，如下所示

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12
OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

#Define functions for each device_type
def type_A(ip):
    return{
        'device_type': 'A',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

def type_B(ip):
    return{
        'device_type': 'B',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

def type_C(ip):
    return{
        'device_type': 'C',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

#Function to create output text file
def writeOutFile(outFileName, string):
    with open(outFileName, "w") as f:
       outfile = f.write(string)

#Open Text file that contain device type and ip address
deviceFile = open('devices.txt','r')

#Create list llist for each line in the file.  
#The first item is the device type, 
#The second item is the IP address
for line in deviceFile:
    llist = line.split()
    ipAd = llist[1]

    #Check the first item of the list to determine device type and set 
    #variables
    if llist[0] == 'A':
        dvs = type_A(ipAd)
        sendCommand = 'command for device type A'
    elif llist[0] == 'B':
        dvs = type_B(ipAd)
        sendCommand = 'command for device type B'
    elif llist[0] == 'C':
        dvs = type_C(ipAd)
        sendCommand = 'command for device type c'
    else:
        print("no valid device type")
        break

    dvs_connect = ConnectHandler(**dvs)
    sendCommand = (dvs_connect.send_command(sendCommand))
    #This print all the devices output on the terminal
    print(sendCommand)

    #Generate output file
    outFileName = "outputFile.txt"

    #function call to write the output string into a text file
    writeOutFile(outFileName, sendCommand)

    dvs_connect.disconnect()

deviceFile.close()

剧本如下

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12
OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

#Define functions for each device_type
def type_A(ip):
    return{
        'device_type': 'A',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

def type_B(ip):
    return{
        'device_type': 'B',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

def type_C(ip):
    return{
        'device_type': 'C',
        'ip': ip,
        'username': 'usr10',
        'password': 'password',
        }

#Function to create output text file
def writeOutFile(outFileName, string):
    with open(outFileName, "w") as f:
       outfile = f.write(string)

#Open Text file that contain device type and ip address
deviceFile = open('devices.txt','r')

#Create list llist for each line in the file.  
#The first item is the device type, 
#The second item is the IP address
for line in deviceFile:
    llist = line.split()
    ipAd = llist[1]

    #Check the first item of the list to determine device type and set 
    #variables
    if llist[0] == 'A':
        dvs = type_A(ipAd)
        sendCommand = 'command for device type A'
    elif llist[0] == 'B':
        dvs = type_B(ipAd)
        sendCommand = 'command for device type B'
    elif llist[0] == 'C':
        dvs = type_C(ipAd)
        sendCommand = 'command for device type c'
    else:
        print("no valid device type")
        break

    dvs_connect = ConnectHandler(**dvs)
    sendCommand = (dvs_connect.send_command(sendCommand))
    #This print all the devices output on the terminal
    print(sendCommand)

    #Generate output file
    outFileName = "outputFile.txt"

    #function call to write the output string into a text file
    writeOutFile(outFileName, sendCommand)

    dvs_connect.disconnect()

deviceFile.close()

devices.txt列表

A 192.168.100.100
A 192.168.100.110
B 10.1.10.100
C 10.2.10.10
C 10.2.10.11
C 10.2.10.12

outputFile.txt 文件输出内容只是最后一行内容…A和B的输出内容似乎已被覆盖

OUTPUT CONTENT for device type C IP 10.2.10.12

我预计我运行脚本的次数会覆盖文本文件的现有内容，但不会重复…如果我的devices.txt列表中有6个设备…这意味着我的文本文件输出中应该有6个设备输出。输出文件如下所示

OUTPUT CONTENT for device type A IP 192.168.100.100
OUTPUT CONTENT for device type A IP 192.168.100.110
OUTPUT CONTENT for device type B IP 10.1.10.100
OUTPUT CONTENT for device type C IP 10.2.10.10
OUTPUT CONTENT for device type C IP 10.2.10.11
OUTPUT CONTENT for device type C IP 10.2.10.12

---

我真的希望有人能帮助我。。请帮忙。谢谢。

使用模式

'w'打开文件将截断文件（如果存在），而模式
'a'
将附加到文件

您的问题是，您正在以模式
'w'
为每行输出重新打开文件。每次重新打开文件时，都会删除以前的内容

此问题有两种解决方案：

首选的解决方案是在脚本中打开文件一次，然后使用现有的文件句柄向其写入多行，而不是为每行输出打开一个新的文件句柄
您也可以在脚本开始时使用mode
'w'
打开文件一次，然后从那时起使用mode
'a'
（但这是一种黑客行为）
实现第一个选项的一种方法是在主循环之前打开文件：

with open("outputFile.txt", "w") as f:
    for line in deviceFile:
        # ...

        # Replace this line:
        # writeOutFile(outFileName, sendCommand)
        # With this one:
        f.write(sendCommand)

在写入此字符串之前，您可能需要将换行符（
“\n”
）追加到此字符串；我看不出
dvs\u connect.send\u command（）
如何格式化其输出。
问题不在于以不同的模式打开文件，你可以做的是将文件信息保存在pickle文件中，当你运行它时，如果你想存储设备的ip，请检查它是否存在于pickle dump文件中，如果是这样的话，跳过else写入文本文件，并在最后用输出更新pickle文件Hanks先生…你能展示一下它是如何完成的吗？谢谢你的回答先生…选项1是我尝试做的。。。我已经尝试过在for循环中打开文件，但还没有在for循环之前打开文件…感谢您的回复和示例。我试试这个。