向字典添加元素时抛出KeyError异常 - Python3.5.3

Let's break down what's going wrong and how to fix it, starting with the root cause of your KeyError.

First: Understand Why the KeyError Happens #

A KeyError almost always means you're trying to access a key that doesn't exist in your dictionary. Looking at your code snippet, I notice two potential issues right away:

1. You initialized decoded_data as a list ([HexDecode(data[0]), HexDecode(data[1])]), but later you're trying to access it like a dictionary (e.g., decoded_data.ap...). Lists use index numbers, not named keys—mixing these up will definitely cause errors.
2. If you did intend decoded_data to be a dictionary, you might be trying to access a key you never defined, or trying to assign to a key in a way that assumes it already exists.

Practical Solutions to Fix the KeyError #

1. Fix the Data Structure Confusion (Most Likely Fix) #

If decoded_data is supposed to store metadata like title, artist, etc., it should be a dictionary, not a list. Rewrite your initialization to use key-value pairs:

# Initialize as a dictionary with required fields
decoded_data = {
    "title": HexDecode(data[0]),
    "artist": HexDecode(data[1])
}

# Add optional fields only if data exists
if len(data) == 4:
    decoded_data["album"] = HexDecode(data[2])
    decoded_data["track_number"] = HexDecode(data[3])  # Example of another optional field

This way, you're explicitly defining keys and adding new ones safely—assigning to a new key in a dictionary doesn't throw a KeyError, only accessing an undefined one does.

2. Use dict.get() for Safe Key Access #

If you need to access a key that might not exist (e.g., optional metadata fields), use the get() method instead of direct bracket access. It returns a default value (like None or a custom placeholder) instead of throwing an error:

# Get album info, or return "Unknown Album" if the key doesn't exist
album_name = decoded_data.get("album", "Unknown Album")

3. Check if a Key Exists Before Accessing #

If you want to handle missing keys with custom logic, use the in operator to verify the key exists first:

if "album" in decoded_data:
    print(f"Album: {decoded_data['album']}")
else:
    print("No album metadata available")

4. Initialize Default Keys Upfront #

If certain fields should always be present (even if empty), define them when creating the dictionary:

decoded_data = {
    "title": HexDecode(data[0]),
    "artist": HexDecode(data[1]),
    "album": "Unknown",
    "genre": "Unknown"
}

# Override defaults only if data is available
if len(data) >= 4:
    decoded_data["album"] = HexDecode(data[2])

Bonus: Improve Your File Parsing Logic #

I also noticed a small issue with how you're reading the metadata file. Right now, you only process the data if the final line ends with m>—you might miss earlier complete chunks of metadata. Move the processing logic inside the loop to handle each complete line as it's found:

def metadataScrape():
    current_line = ""
    with open("/tmp/shairport-sync-metadata") as f:
        for line in f:
            current_line += line.rstrip('\n')  # Cleanly remove newline characters
            # Check if we've reached the end of a metadata chunk
            if current_line.endswith("m>"):
                html_data = html.fromstring(current_line)
                data = html_data.xpath("//text()")
                
                # Initialize dictionary correctly here
                decoded_data = {
                    "title": HexDecode(data[0]),
                    "artist": HexDecode(data[1])
                }
                
                if len(data) >= 4:
                    decoded_data["album"] = HexDecode(data[2])
                    decoded_data["extra"] = HexDecode(data[3])
                
                # Reset for the next chunk of metadata
                current_line = ""

内容的提问来源于stack exchange，提问作者Srevilo