Python 检查整数输入
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Python check for integer input
提问by user3353003
I am trying to allow a user to input into my program, however when they enter a string my program fails. It is for a bigger program but was trying to correct the problem, I have so far:
我试图允许用户输入我的程序，但是当他们输入一个字符串时，我的程序失败了。这是一个更大的程序，但试图纠正这个问题，我到目前为止：
data = raw_input('Enter a number: ')
number = eval(data)
if type(number) != int:
print"I am afraid",number,"is not a number"
elif type(number) == int:
if data > 0:
print "The",number,"is a good number"
else:
print "Please enter a positive integer"
when the user enters a string, it returns:
当用户输入一个字符串时，它返回：
number = eval(data)
File "<string>", line 1, in <module>
NameError: name 'hel' is not defined
Any help would be most appreciated.
非常感激任何的帮助。
回答by Maxime Lorant
You're using eval, which evaluate the string passed as a Python expression in the current context. What you want to do is just
您正在使用eval，它评估在当前上下文中作为 Python 表达式传递的字符串。你想做的只是
data = raw_input('Enter a number: ')
try:
number = int(data)
except ValueError:
print "I am afraid %s is not a number" % data
else:
if number > 0:
print "%s is a good number" % number
else:
print "Please enter a positive integer"
This will try to parse the input as an integer, and if it fails, displays the error message.
这将尝试将输入解析为整数，如果失败，则显示错误消息。
回答by t.animal
You can just use int(raw_input())to convert the input to an int.
您可以仅用于int(raw_input())将输入转换为 int。
Never evaluate untrusted user input using eval, this will allow a malicious user to take over your program!
永远不要使用 eval 评估不受信任的用户输入，这将允许恶意用户接管您的程序！
回答by angelcool.net
Why is no one mentioning regular expressions ? The following works for me, adjust the regex to fit your needs.
为什么没有人提到正则表达式？以下对我有用，调整正则表达式以满足您的需求。
[aesteban@localhost python-practice]$ cat n.py
import re
userNumber = ''
while not re.match('^-?[0-9]*\.?[0-9]+$',userNumber):
userNumber = raw_input("Enter a number please: ")
newNumber = float(userNumber) + 100
print "Thank you!! Your number plus 100 is: " + str(newNumber)
Tests:
测试：
[aesteban@localhost python-practice]$ python n.py
Enter a number please: I want to make 0 an hour.
Enter a number please: ok ok...
Enter a number please: 200
Thank you!! Your number plus 100 is: 300.0
[aesteban@localhost python-practice]$ python n.py
Enter a number please: -50
Thank you!! Your number plus 100 is: 50.0
[aesteban@localhost python-practice]$ python n.py
Enter a number please: -25.25
Thank you!! Your number plus 100 is: 74.75
