Python字典,变量作为键

Question

我是一个Python新手试图解析一个文件来制作一个内存分配表.我的输入文件格式如下:

48 bytes allocated at 0x8bb970a0
24 bytes allocated at 0x8bb950c0
48 bytes allocated at 0x958bd0e0
48 bytes allocated at 0x8bb9b060
96 bytes allocated at 0x8bb9afe0
24 bytes allocated at 0x8bb9af60    

我的第一个目标是创建一个表来计算特定数量的字节分配的实例.换句话说,我对上面输入的所需输出将是这样的:

48 bytes -> 3 times
96 bytes -> 1 times
24 bytes -> 2 times

(现在,我不关心内存地址)

由于我正在使用Python,我认为使用字典这样做是正确的方法(基于大约3个小时的阅读Python教程).这是一个好主意吗？

在尝试使用字典时,我决定将字节数设为'key',将计数器设为'value'.我的计划是在每次出现钥匙时递增计数器.截至目前,我的代码段如下:

# Create an empty dictionary
allocationList = {}

# Open file for reading
with open("allocFile.txt") as fp: 
    for line in fp: 
        # Split the line into a list (using space as delimiter)
        lineList = line.split(" ")

        # Extract the number of bytes
        numBytes = lineList[0];

        # Store in a dictionary
        if allocationList.has_key('numBytes')
            currentCount = allocationList['numBytes']
            currentCount += 1
            allocationList['numBytes'] = currentCount
        else
            allocationList['numBytes'] = 1 

for bytes, count in allocationList.iteritems()
    print bytes, "bytes -> ", count, " times"

有了这个,我在'has_key'调用中得到一个语法错误,这让我质疑是否甚至可以将变量用作字典键.到目前为止我看到的所有示例都假设密钥可以预先获得.在我的情况下,我只有在解析输入文件时才能获取密钥.

(请注意,我的输入文件可以运行成数千行,包含数百个不同的键)

感谢您提供任何帮助.

Answer 1

学习语言与语法和基本类型一样,与标准库有关.Python已经有了一个让你的任务非常简单的类:collections.Counter.

from collections import Counter

with open("allocFile.txt") as fp:
    counter = Counter(line.split()[0] for line in fp)

for bytes, count in counter.most_common():
    print bytes, "bytes -> ", count, " times"