Python中列表元素与前一个元素比较及Paramiko多路径执行问题

Let's break down how to do this—there are a few simple, readable approaches depending on what you need to achieve with the comparison:

Basic For Loop (Great for Actionable Comparisons) #

If you need to perform specific actions based on the comparison (like printing results or modifying elements), a straightforward loop is easy to follow:

my_list = [1, 3, 2, 5, 4]

# Start from index 1 since the first element has no prior element
for i in range(1, len(my_list)):
    current = my_list[i]
    previous = my_list[i-1]
    
    # Example: Check if current element is larger than the previous one
    if current > previous:
        print(f"Current value {current} is bigger than {previous}")
    else:
        print(f"Current value {current} is smaller or equal to {previous}")

List Comprehension (Concise for Boolean Results) #

If you just want a list of boolean outcomes (e.g., whether each element is greater than the prior), list comprehension is perfect:

my_list = [1, 3, 2, 5, 4]
# Pair each element with its predecessor using zip()
comparison_results = [current > previous for current, previous in zip(my_list[1:], my_list)]
print(comparison_results)  # Output: [True, False, True, False]

Using Enumerate (For Index + Value Access) #

If you need both the index and value of elements during comparison, enumerate is a handy tool:

my_list = [1, 3, 2, 5, 4]
for idx, current in enumerate(my_list):
    if idx == 0:
        continue  # Skip first element—it has no predecessor
    previous = my_list[idx-1]
    print(f"At index {idx}: {current} vs {previous}")

Looking at your code, I spot two key problems that are causing your parsing headaches. Let's fix them step by step:

Problem 1: Passing a list to sftp.listdir() #

The sftp.listdir() method expects a single string path, not a list of paths. You need to loop through your path list one entry at a time.

Problem 2: Unnecessary use of exec_command for listing files #

You don't need to run an SSH shell command to list files—SFTP has its own built-in methods to fetch directory contents, which are more reliable and avoid messy shell output parsing.

Corrected Code #

Here's the fixed version that works as intended:

import paramiko

client = paramiko.SSHClient()
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
client.connect('hostname', username='test1234', password='test')

paths = ['/home/test/', '/home/test1/','/home/test3/']
sftp = client.open_sftp()

for path in paths:
    try:
        # Use SFTP's native listdir() to get files in the current path
        filenames = sftp.listdir(path)
        print(f"Files in {path}:")
        for filename in filenames:
            # Get full path if needed (avoids trailing slash issues)
            full_path = f"{path.rstrip('/')}/{filename}"
            print(full_path)
    except Exception as e:
        # Add error handling for missing paths or permission issues
        print(f"Failed to access {path}: {str(e)}")

# Clean up connections to avoid resource leaks
sftp.close()
client.close()

Key Improvements: #

• Loops through each path individually instead of passing the entire list to listdir()
• Uses SFTP's native file-listing method instead of shell commands (no more parsing stdout)
• Adds basic error handling for common issues like missing directories
• Properly closes SFTP and SSH connections when done

If you specifically need to run a shell command for each file (not just list them), you'd adjust the code to pass the full file path to exec_command—but for listing files, SFTP is the cleaner, more reliable choice.

内容的提问来源于stack exchange，提问作者Victory