打开文件并读取数据

Question

So I am using these lines of code to read an Excel file.

fin=open("C:\Users\Student\Desktop\Python Coding\bodyfat.csv",'rU')
fin.readline()

However I keep getting this error statement and I have no idea what is going on

>>> fin=open("C:\Users\Student\Desktop\Python Coding\bodyfat.csv",'rU')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 22] invalid mode ('rU') or filename: 'C:\\Users\\Student\\Desktop\\Python Coding\x08odyfat.csv'
>>> fin.readline()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'fin' is not defined

Any idea on what is going on here?

Answer 1

You are not escaping string backslashes properly. Notice in the traceback it says "Coding\\x08odyfa". You can use raw strings

r"C:\Users\Student\Desktop\Python Coding\bodyfat.csv"

or escape the escape char

"C:\\Users\\Student\\Desktop\\Python Coding\\bodyfat.csv"

Answer 2

The first error occurs because, in standard Python strings, backslashes do interesting things to the characters that follow them (see the documentation on string literals for details):

>>> "C:\Users\Student\Desktop\Python Coding\bodyfat.csv"
'C:\\Users\\Student\\Desktop\\Python Coding\x08odyfat.csv'
                                         # ^ what?

The second error occurs because, after the first error occurs, fin is never assigned.

The simplest fix is to use "raw strings", prefixed with an r , to indicate that backslashes should be treated as normal characters:

>>> r"C:\Users\Student\Desktop\Python Coding\bodyfat.csv"
'C:\\Users\\Student\\Desktop\\Python Coding\\bodyfat.csv'

(Don't worry about the doubling, that's just Python's way of indicating that those are literal backslashes, rather than escaping the characters that follow.)

Also, you should use the with "context manager" for file handling:

with open(r"...") as fin:
    line = fin.readline()
    ...