本週講了基本的文字檔案操作

首先是開啟檔案的函式open()，值得注意的是open()返回的不是全部檔案內容（記憶體可能吃不下），而是操作連結記憶體與因硬碟檔案的handle，起到一個connection的作用

然後文字檔案中每一行字元的末尾是換行字元“/n”（這是一個字元），注意print函式執行完也會新增一個“/n”字元，可能會有重複換行的問題。當遇到此問題要用strip()函式清楚字元首尾的“/n”字元

fh = open(words.txt)
for line in fh

inp = fh.read()

 可以用if string.startswith()篩選或者過濾特定行。

用raw_input()輸入檔名。

本次有兩個作業，分別是

7.1 Write a program that prompts for a file name, then opens that file and reads through the file, and print the contents of the file in upper case. Use the filewords.txt to produce the output below.

# Use words.txt as the file name
fname = raw_input("Enter file name: ")
fh = open(fname)
inp = fh.read()
inp = inp.upper()
inp = inp.rstrip()


print inp
 

X-DSPAM-Confidence:    0.8475

You can download the sample data at http://www.pythonlearn.com/code/mbox-short.txtwhen you are testing below enter mbox-short.txt as the file name.

答案

# Use the file name mbox-short.txt as the file name
fname = raw_input("Enter file name: ")
fh = open(fname)
count = 0
sum = 0
ave = 0
for line in fh:
    if not line.startswith("X-DSPAM-Confidence:") : continue
    space = line.find(" ")
    raw_num = line[space:]
    num = raw_num.strip()
    num = num.strip()
    num = float(num)
    count = count+1
    sum = sum+num

ave = sum/count
print "Average spam confidence:",ave