Python：讀取文件並計算總和和平均值

Question

問題是逐行讀取文件，然后計算並顯示文件中所有有效數字的總和和平均值。

文本文件是

contains text
79.3
56.15
67
6
text again 
57.86
6
37.863
text again 
456.675

到目前為止，這就是我所擁有的。

numbers = open('fileofnumbers.txt', 'r')

line = file_contents.readline()

numbers.close()

try:
    sum = line + line
    line = file_contents.readline()
    print "The sum of the numbers is", sum


except ValueError:
    print line

Answer 1

使用with符號可以使處理文件更加直觀。

例如，將打開和關閉更改為此：

summation = 0

# Within the with block you now have access to the source variable
with open('fileofnumbers.txt', 'r') as source:
    for line in source: #iterate through all the lines of the file 
        try:
            # Since files are read in as strings, you have to cast each line to a float
            summation += float(line)
        except ValueError:
            pass

可能會讓您開始

如果您想變得更聰明一點，有一個方便的python函數叫做isdigit ，它檢查字符串是否都是整數值，它可以讓您執行以下非常聰明的操作：

is_number = lambda number: all(number.split('.').isdigit())
answer = [float(line) for line in open('fileofnumbers.txt') if is_number(line)]

然后，求和和平均就變得微不足道了：

print sum(answer) # Sum
print sum(answer)/len(answer) #Average

Answer 2

讓我們嘗試使用try-except列出理解。 這可能是一個矯kill過正的方法，但肯定是一個可以放在口袋中的好工具，首先，您需要編寫一個使錯誤消失的函數，例如http://code.activestate.com/recipes/576872-exception-handling-in-a -單行/ 。

然后，您可以像在Unix中一樣通過傳入argv來使用列表argv ：

intxt = """contains text
29.3423
23.1544913425
4
36.5
text again 
79.5074638
3
76.451
text again 
84.52"""

with open('in.txt','w') as fout:
    fout.write(intxt)

def safecall(f, default=None, exception=Exception):
    '''Returns modified f. When the modified f is called and throws an
    exception, the default value is returned'''
    def _safecall(*args,**argv):
        try:
            return f(*args,**argv)
        except exception:
            return default
    return _safecall

with open('in.txt','r') as fin:
    numbers = [safecall(float, 0, exception=ValueError)(i) for i in fin] 
    print "sum:", sum(numbers)
    print "avg:", sum(numbers)/float(len(numbers))

[OUT]：

sum: 336.475255142
avg: 30.5886595584