Python 3.5.2 FileNotFoundError: [Errno 2] 没有这样的文件或目录：'test.txt'

Question

Here is a sample of the code that's causing my issue:

import string

letters = string.ascii_lowercase       

offset = ord('a')


def countFrequency(file_handle):
"""Traverse a file and compute the number of occurences of each letter
return results as a simple 26 element list of integers."""
results = [0] * len(letters)     
for line in file_handle:   #read line from file
    for char in line:      #read char by char from above line
        char = char.lower()    #cnverting char in lowercase
        if char in letters:    #checking if char exist i letters
            results[ord(char) - offset] += 1

return results


#sorting the both lists frequency and letter list    
def sort(ltr,frequency):
for x in xrange(len(frequency)):
    for y in xrange(len(frequency)-1):
        if frequency[y]<frequency[y+1]: # on true swap values
            t=frequency[y+1]
            frequency[y+1]=frequency[y]
            frequency[y]=t
            t=ltr[y+1]
            ltr[y+1]=ltr[y]
            ltr[y]=t

#print the sorted results
for i in xrange(len(ltr)):
    if(frequency[i]==0):
        break;
    print "%s=%d" % (ltr[i], frequency[i])



if __name__ == "__main__":
filename = str(input('Enter file name(e.g. test.txt):'))
#file path
sourcedata = open(filename)
#fucntion return frequency of letters
frequency = countFrequency(sourcedata)
#creating list of letters (a-z) 
ltrs= [0] * len(letters)
for i in xrange(len(frequency)):
   ltrs[i]=chr(i + ord('a'))
#sorting the result in descending order
sort(ltrs,frequency)

I am supposed to write a Python program that prompts for an input filename. The program should open the named file and calculate the frequency of each letter in it, ignoring case. The resulting table should be output to the screen in sorted order. By “sorted order” I mean that the most frequent letter should be displayed first, followed by the second most frequent letter, and so on. This is what I got so far but when I try running it and inputting the filename I receive:

sourcedata = open(filename) #file path FileNotFoundError: [Errno 2] No such file or directory: 'filename'

What could be casing this error? How do I resolve this issue?

Answer 1

Providing you're using the full, correct path, you can try:

import os
filename = input('Enter file name(e.g. test.txt):')
filename = os.path.join(filename)
sourcedata = open(filename)

Additionally, if you're using Python 3+, print "%s=%d" % (ltr[i], frequency[i]) , will not work; it should be:

print('{}={}'.format(ltr[i], frequency[i]))

Answer 2

Use the absolute path (use /Path/to/your/file.txt instead of file.txt). Using the absolute path is much better than using the relative path because you will not get the FileNotFoundError and it will work in Python 2 and in Python 3. As @Trenton_m has said,

print "%s=%d" % (ltr[i], frequency[i])

will not work in python 3. You should use:

print('{}={}'.format(ltr[i], frequency[i]))