python：系统未定义
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python: sys is not defined
提问by astrochris
I have a piece of code which is working in Linux, and I am now trying to run it in windows, I import sys but when I use sys.exit(). I get an error, sys is not defined. Here is the begining part of my code
我有一段在 Linux 中工作的代码，我现在试图在 Windows 中运行它，我导入了 sys 但当我使用 sys.exit() 时。我收到一个错误，sys 未定义。这是我的代码的开始部分
try:
import numpy as np
import pyfits as pf
import scipy.ndimage as nd
import pylab as pl
import os
import heapq
import sys
from scipy.optimize import leastsq
except ImportError:
print "Error: missing one of the libraries (numpy, pyfits, scipy, matplotlib)"
sys.exit()
Why is sys not working??
为什么系统不工作？
采纳答案by Martijn Pieters
Move import sysoutsideof the try-exceptblock:
移动import sys以外的中try-except块：
import sys
try:
# ...
except ImportError:
# ...
If any of the imports beforethe import sysline fails, the restof the block is not executed, and sysis never imported. Instead, execution jumps to the exception handling block, where you then try to access a non-existing name.
如果该行之前的任何导入import sys失败，则不会执行该块的其余部分，并且sys永远不会导入。相反，执行跳转到异常处理块，然后您尝试访问一个不存在的名称。
sysis a built-in module anyway, it is alwayspresent as it holds the data structures to track imports; if importing sysfails, you have bigger problems on your hand (as that would indicate that allmodule importing is broken).
sys无论如何，它是一个内置模块，它始终存在，因为它拥有跟踪导入的数据结构；如果导入sys失败，则说明您手头有更大的问题（因为这表明所有模块导入都已损坏）。
回答by TerryA
You're trying to import all of those modules at once. Even if one of them fails, the rest will not import. For example:
您正在尝试一次导入所有这些模块。即使其中一个失败，其余的也不会导入。例如：
try:
import datetime
import foo
import sys
except ImportError:
pass
Let's say foodoesn't exist. Then only datetimewill be imported.
假设foo不存在。然后只会datetime被导入。
What you can do is import the sys module at the beginning of the file, before the try/except statement:
您可以做的是在文件开头的 try/except 语句之前导入 sys 模块：
import sys
try:
import numpy as np
import pyfits as pf
import scipy.ndimage as nd
import pylab as pl
import os
import heapq
from scipy.optimize import leastsq
except ImportError:
print "Error: missing one of the libraries (numpy, pyfits, scipy, matplotlib)"
sys.exit()
回答by astrognocci
I'm guessing your code failed BEFORE import sys, so it can't find it when you handle the exception.
我猜你的代码在导入系统之前失败了，所以当你处理异常时它找不到它。
Also, you should indent the your code whithin the tryblock.
此外，您应该在try块中缩进您的代码。
try:
尝试：
import sys
# .. other safe imports
try:
import numpy as np
# other unsafe imports
except ImportError:
print "Error: missing one of the libraries (numpy, pyfits, scipy, matplotlib)"
sys.exit()
