Python if语句使用CSV数据

问题描述

我正在从CSV文件中读取一些数据，然后根据if语句打印一个值，但似乎没有意义。我希望它会打印等于1

I am reading in some data from a CSV file and then printing a value based on an if statement, but it doesn't seem to make sense to me. I would expect it would print equal to 1

PYTHON代码：

import csv

#open CSV file
csvfile = open("C:\\python.csv", "rb")
data = csv.reader(csvfile)
data = [row for row in data]

#start loop through each item
for currentrow in range(1, 2):  # numbers off due to array starting at 0
    #grab one record data [row][col]
    Count = data[currentrow][7]

    print "Count equals: " + Count

    if Count > 1:
        print "greater than 1"
    if Count == 1:
        print 'equal to 1'

OUTPUT：

Count equals: 1.00
greater than 1

推荐答案

您的麻烦来自于您从文件总是一个字符串（即 str type）。这意味着即使文件包含一个数字，它也会作为字符串读入您的变量。因此，如果您的文件如下所示：

Your trouble stems from the fact that what you read from a file is always a string (i.e. str type). This means that even if the file contains a number, it is read into your variable as a string. Therefore, if your file looks like this:

myFile.txt ：

2

如果您：

with open('myFile.txt') as infile:
    x = infile.readline()

那么 x 会有值'2' code>，这是一个 str 类型。这意味着，如果你 x * 2 ，你会得到 '22'，因为这是字符串乘法

then, x would have the value '2', which is a str type. This means, that if you did x*2, you'd get '22', because that's how strings multiply out.

你真正想要的是将该sting转换为 int 。这称为将字符串转换为整数，可以非常简单：

What you really want, is to convert that sting into an int. This is called "casting a string into an integer" and can be done very simply:

y = int(x)

还有一个你应该注意的类型： float 。它用于保存十进制数。所以，如果你说

There's another type that you should be aware of: float. It is used to hold decimal numbers. So, if you were to say

x = 3.4

那么 x 将是 float 。您还可以将 int 转换为 float s：

then x would be a float. You can also cast ints to floats:

z = float(y)

会将 z 转换为浮点值， 2.0

您的实际问题：

data = [row for row in data]  # data is now a list of lists; each sublist is a list of strings
for currentrow in range(1,2):
    Count = data[currentrow][7]  # Count is now the string at index 7, of the sublist at index `currentrow`, i.e. 1.00
    Count = float(Count)  # Count is now the floating point value of the string '1.00'
    Count = int(Count)  # Count is now the integer value of 1.00, i.e. 1
    if Count > 1:
        print "greater than 1"
    if Count == 1:
        print "equal to 1"

现在，您的第二个问题：

Now, onto your second problem:

print 'Count equals ' + Count

这里，您正在尝试添加 str 和 int 。那么，这些是不兼容的类型添加。因此，您应该将 int 转换为 str ;就像 str 可以转换为 int s， int 可以通过调用 str（）转换为 str s：

Here, you are trying to add a str and an int. Well, those are incompatible types for addition. Therefore, you should cast the int into a str; and just like how strs can be cast into ints, ints can be cast into strs with a call to str():

Count_str = str(Count)

所以，当你打印的值，你可以做：

So when you want to print the value, you could do:

print "Count equals " + str(Count)

当然，print语句更友好一些， p>



Of course, the print statement is a little more friendly and lets you do something like this:

print "Count equals", Count  # no casting needed here

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