与 While 循环一起使用时，如果没有flush=True，打印函数将无法工作

Question

是否存在一些已知问题，即 Azure Runbooks 的 Python 环境不喜欢将

while

循环函数与

print

函数结合使用而不附加

flush=True

？

当

while

一词包含在

main

函数中时，我没有看到返回任何打印语句。

这旨在每当我的 Azure VM 的状态发生变化时发送警报。 （这将通过电子邮件进行，但为了方便起见，我刚刚包含了打印语句......这应该有效）

删除

while

功能，所有打印语句都会出现。

这是一个非常愚蠢的情况。即使

print("Can you see this message....")

和

print("Entering loop...")

也不会打印。这些

print

语句甚至不会在

while

循环中打印，因此即使

while

循环的执行存在问题（实际上不存在），它也应该打印。我会通过调试打印向您展示，但如果实际打印的内容像我告诉的那样，那么您就可以看到。

我的血压因此而严重升高。

compute_client

已通过身份验证，并且它返回正确的

vm_name

，那么为什么 - 每当我包含

while

循环时 - 它是否有嘶嘶声？

我对此非常生气。

import time, random, smtplib, inspect, string
from datetime import datetime
from email.mime.text import MIMEText
from azure.common.credentials import ServicePrincipalCredentials
from azure.mgmt.compute import ComputeManagementClient

# Azure setup
subscription_id = 'xxx'  
resource_group_name = 'xxx'  
vm_name = 'xxx'  

from azure.core.exceptions import ClientAuthenticationError

# Authentication of Azure's Service Principal
def service_principal_authentication():
    """Checks the Authentication of Azure's Service Principal """
    print("Authenticating Service Principal....")
    try:
        credentials = ServicePrincipalCredentials(
            client_id='xxx',
            secret='xxx',
            tenant='xxx'
        )
        print("Service Principal Authenticity Verified")
        return ComputeManagementClient(credentials, subscription_id)
    except Exception as e:
        print(f"There was an error with the authenticating the Service Principal: {e}")
    except ClientAuthenticationError as e:
        print(f"Client Authentication Error {e}")

# Email setup
sender_email = 'xxx'  
receiver_email = 'xxxx' 
smtp_server = 'xxx'   
smtp_port = 587
smtp_password = 'xxx'  

def send_notification(subject, body):
    """Send an email notification."""
    msg = MIMEText(body)
    msg['Subject'] = subject
    msg['From'] = sender_email
    msg['To'] = receiver_email

    try:
        with smtplib.SMTP(smtp_server, smtp_port) as server:
            server.starttls()
            server.login(sender_email, smtp_password)
            server.sendmail(sender_email, receiver_email, msg.as_string())
            print("Email sent successfully!")
    except Exception as e:
        print(f"{e} in ", inspect.stack()[0].function)

def get_vm_status(compute_client):
    """Retrieve the current status of the VM."""
    print("Retrieving VM status......")
    try:
        # Explicitly request the instance view
        vm = compute_client.virtual_machines.get(resource_group_name, vm_name, expand='instanceView')
        
        # Check if instance view is available
        if vm.instance_view:
            print(f"Can you see this message? {inspect.stack()[0].function}")
            return vm.instance_view.statuses[1].code  # Assuming the status is at index 1
        else:
            print("Instance view is not available.")
            return None
        
    except ClientAuthenticationError as e:
        print(f"There was a client authentication error {e}")
    except Exception as e:
        print(f"Error retrieving VM status: {e}, in function {inspect.stack()[0].function}")

def generate_incident_reference_number():
    incident_timestamp = datetime.utcnow().strftime("%Y%m%d%H%M%S")
    incident_number = ''.join(random.choices(string.ascii_uppercase + string.digits, k=10))
    return f"INC{incident_timestamp}{incident_number}"

def log_to_azure_monitor():
    pass

def main():
    print("Entering loop.....",flush=True)
    while True:
        compute_client = service_principal_authentication()
        previous_vm_status = None
        current_vm_status = get_vm_status(compute_client)

        if current_vm_status != previous_vm_status:
            incident_number = generate_incident_reference_number()
            print(f"This has changed {current_vm_status} - {previous_vm_status} - {incident_number}", flush=True)
        else:
            print(f"This has remained the same {current_vm_status}", flush=True)
        previous_vm_status = current_vm_status
        time.sleep(10)

if __name__ == "__main__":
    main()

Answer 1

如前所述，Azure Runbook 具有输出缓冲，这有时会阻止循环内立即显示打印语句。

即使您将
• flush=True

  添加到

  print

  ，循环也可能会连续运行，导致输出缓冲无法及时刷新。尝试添加额外的

  flush

  调用，或者考虑记录日志而不是使用

  print

  。

删除
• while True

  循环并使用有限循环或限时循环进行测试，看看是否可以隔离问题。

打印也不是。代码已根据您的建议进行了更新，以便您可以看到我放置附加打印语句的位置。

脚本可能会在

到达

get_vm_status函数之前或在执行函数本身时阻塞。

首先在调用 

print

之前添加一个

get_vm_status

 语句来检查它是否被调用。然后，在 

get_vm_status

 函数中，在每个主要操作之前放置打印以跟踪其执行情况。

更新代码：

import time
import random
import smtplib
import inspect
import string
from datetime import datetime
from email.mime.text import MIMEText
from azure.common.credentials import ServicePrincipalCredentials
from azure.mgmt.compute import ComputeManagementClient
from azure.core.exceptions import ClientAuthenticationError

# Azure setup
subscription_id = 'xxx'  
resource_group_name = 'xxx'  
vm_name = 'xxx'  

# Authentication of Azure's Service Principal
def service_principal_authentication():
    """Checks the Authentication of Azure's Service Principal """
    print("Authenticating Service Principal....")
    try:
        credentials = ServicePrincipalCredentials(
            client_id='xxx',
            secret='xxx',
            tenant='xxx'
        )
        print("Service Principal Authenticity Verified")
        return ComputeManagementClient(credentials, subscription_id)
    except Exception as e:
        print(f"There was an error with the authenticating the Service Principal: {e}")
    except ClientAuthenticationError as e:
        print(f"Client Authentication Error {e}")

# Email setup
sender_email = 'xxx'  
receiver_email = 'xxxx' 
smtp_server = 'xxx'   
smtp_port = 587
smtp_password = 'xxx'  

def send_notification(subject, body):
    """Send an email notification."""
    msg = MIMEText(body)
    msg['Subject'] = subject
    msg['From'] = sender_email
    msg['To'] = receiver_email

    try:
        with smtplib.SMTP(smtp_server, smtp_port) as server:
            server.starttls()
            server.login(sender_email, smtp_password)
            server.sendmail(sender_email, receiver_email, msg.as_string())
            print("Email sent successfully!")
    except Exception as e:
        print(f"{e} in ", inspect.stack()[0].function)

def get_vm_status(compute_client):
    """Retrieve the current status of the VM."""
    print("Entering get_vm_status function.....", flush=True)
    try:
        print("Retrieving VM status......", flush=True)
        # Explicitly request the instance view
        vm = compute_client.virtual_machines.get(resource_group_name, vm_name, expand='instanceView')
        
        # Check if instance view is available
        if vm.instance_view:
            print(f"Can you see this message? {inspect.stack()[0].function}", flush=True)
            return vm.instance_view.statuses[1].code  # Assuming the status is at index 1
        else:
            print("Instance view is not available.", flush=True)
            return None
        
    except ClientAuthenticationError as e:
        print(f"There was a client authentication error {e}", flush=True)
    except Exception as e:
        print(f"Error retrieving VM status: {e}, in function {inspect.stack()[0].function}", flush=True)

def generate_incident_reference_number():
    incident_timestamp = datetime.utcnow().strftime("%Y%m%d%H%M%S")
    incident_number = ''.join(random.choices(string.ascii_uppercase + string.digits, k=10))
    return f"INC{incident_timestamp}{incident_number}"

def log_to_azure_monitor():
    pass

def main():
    print("Entering loop.....", flush=True)
    while True:
        print("Before calling get_vm_status....", flush=True)  # Debug print before calling the function
        compute_client = service_principal_authentication()
        previous_vm_status = None
        current_vm_status = get_vm_status(compute_client)

        if current_vm_status != previous_vm_status:
            incident_number = generate_incident_reference_number()
            print(f"This has changed {current_vm_status} - {previous_vm_status} - {incident_number}", flush=True)
        else:
            print(f"This has remained the same {current_vm_status}", flush=True)
        previous_vm_status = current_vm_status
        time.sleep(10)

if __name__ == "__main__":
    main()

如果 

"Before calling get_vm_status...."

没有出现，则问题出在
• compute_client

   或 

  service_principal_authentication()

   方法的初始化。

  如果 

  "Retrieving VM status......"
未出现，则问题出在检索虚拟机状态的 API 调用中。

• 如果 

  "Can you see this message?"
未打印，则该函数可能未按预期返回或完成。