Loop through each items

When to use loop for each item in list

Great follow-up, Pavan! 👏 Let’s break down when to use a loop to go through each item in a list, especially from a DevOps and automation point of view.

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✅ When to use a loop for each item in a list

You use a for loop when you want to do the same action on multiple items, one by one.

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🔧 Real-world DevOps Use Cases:

Use Case	Why loop?
🔁 Restart services on multiple servers	You have a list of server IPs and want to send a command to each
🐳 Stop multiple Docker containers	You have a list of container names to act on
☸️ Apply Kubernetes manifests in multiple namespaces	You want to repeat the kubectl apply command for each namespace
📂 Back up several databases	Each database name in the list needs a pg_dump
🔍 Health check multiple URLs	Each URL should be pinged or checked
🚀 Deploy multiple modules in Terraform	You need to cd into each module directory and run terraform apply

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🔄 Basic Format:

items = ["item1", "item2", "item3"]
for item in items:
    # do something with item
    print(item)

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✅ When to Use a Loop:

Situation	Use a Loop?
Same action needs to run for multiple items	✅ Yes
You’re working with a list/array	✅ Yes
You’re automating repetitive tasks	✅ Yes
You want to avoid repeating code manually	✅ Yes

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❌ When not to use a loop:

Situation	Why not use a loop?
You only need to process one item	A loop adds unnecessary complexity
You need parallel or asynchronous processing	Use threading or async instead
You want to break early after a match	Maybe use a loop with break or an if instead

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🔁 Example from DevOps:

# Restart nginx on multiple servers
servers = ["10.0.0.1", "10.0.0.2", "10.0.0.3"]

for ip in servers:
    subprocess.run(f"ssh ubuntu@{ip} 'sudo systemctl restart nginx'", shell=True)

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✅ Summary:

Question	Answer
When should I use a loop over a list?	When you're performing repetitive actions on each element
What kind of data works well?	Lists, arrays, sets — anything iterable
Should I use enumerate() too?	Only if you need the index/position of the item

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Let me know if you want to convert one of your tasks (like restart, deploy, backup) into a real Python loop example!

loop through each item of the list using enumerate

# Define a list of names
names = ["Alice", "Bob", "Charlie"]

# Use enumerate to loop through the list with both index (i) and value (name)
# The second argument '1' makes the index start from 1 instead of 0
for i, name in enumerate(names, 1):
    # Print the index and the name in a formatted string
    print(f"{i}. Name is {name}")

# List of server IP addresses
servers = ["10.0.0.1", "10.0.0.2", "10.0.0.3"]

# Loop with enumerate to get both index and IP
for i, ip in enumerate(servers):
    if i == 1:  # Only target the second server (index starts from 0)
        subprocess.run(f"ssh ubuntu@{ip} 'sudo systemctl restart nginx'", shell=True)

without enumerate

servers = ["10.0.0.1", "10.0.0.2", "10.0.0.3"]
for ip in servers:
    subprocess.run(f"ssh ubuntu@{ip} 'sudo systemctl restart nginx'", shell=True)

When to use enumerate or not

Great question, Pavan! 🙌 Understanding when to use enumerate() and when not is a simple but powerful skill — especially in scripting and automation like DevOps.

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✅ Use enumerate() when:

🎯 Situation	🔍 Reason
You need the index/position of the item	e.g., to skip the first item, or process only the 2nd
You want to number items in output	e.g., 1. Server is up, 2. Server is down
You need to reference list position + value together	e.g., Server-1: 10.0.0.1
You're generating unique names based on position	e.g., nginx_log_1.txt, nginx_log_2.txt
You're making conditional logic based on position	e.g., restart only the 3rd container

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🔧 Example:

for i, container in enumerate(containers, 1):
    print(f"Stopping container-{i}: {container}")
    subprocess.run(f"docker stop {container}", shell=True)

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❌ Don't use enumerate() when:

🚫 Situation	🔍 Reason
You only need the values, not their positions	Index adds unnecessary complexity
You're not using the index at all in your loop body	Cleaner code = better code
You're using dictionaries (use .items() instead)	enumerate() is for sequences like lists/tuples

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🔧 Example without enumerate():

for ip in servers:
    subprocess.run(f"ssh ubuntu@{ip} 'sudo systemctl restart nginx'", shell=True)

Here, the index doesn't matter — just loop and act.

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🔁 Quick Decision Chart:

Do you need index (position)?	Use enumerate()?
❌ No	❌ No
✅ Yes	✅ Yes

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💡 Pro Tip for DevOps:

In deployment, logging, and automation, if your logic or file naming depends on position, enumerate() is your best friend.

Let me know if you want a cheatsheet image or a downloadable version of this!

looping command and collecting logs

import subprocess

# List of server IPs
servers = ["10.0.0.1", "10.0.0.2", "10.0.0.3"]

# Dictionary to store output for each server
output_log = {}

# Loop through each server
for ip in servers:
    # Run the SSH command and capture output
    result = subprocess.run(
        f"ssh ubuntu@{ip} 'sudo systemctl restart nginx'",
        shell=True,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE
    )

    # Decode and store stdout and stderr
    output_log[ip] = {
        "stdout": result.stdout.decode().strip(),
        "stderr": result.stderr.decode().strip(),
        "returncode": result.returncode
    }

# Print summary
for ip, logs in output_log.items():
    print(f"\n📡 Server: {ip}")
    print(f"✅ Output:\n{logs['stdout']}")
    print(f"⚠️ Error (if any):\n{logs['stderr']}")
    print(f"🔄 Return code: {logs['returncode']}")