I’m working with a .txt file. I want a string of the text from the file with no non-ASCII characters. However, I want to leave spaces and periods. At present, I’m stripping those too. Here’s the code:

def onlyascii(char):
    if ord(char) < 48 or ord(char) > 127: return ''
    else: return char

def get_my_string(file_path):
    f=open(file_path,'r')
    data=f.read()
    f.close()
    filtered_data=filter(onlyascii, data)
    filtered_data = filtered_data.lower()
    return filtered_data

How should I modify onlyascii() to leave spaces and periods? I imagine it’s not too complicated but I can’t figure it out.

You can filter all characters from the string that are not printable using string.printable, like this:

>>> s = "some\x00string. with\x15 funny characters"
>>> import string
>>> printable = set(string.printable)
>>> filter(lambda x: x in printable, s)
'somestring. with funny characters'

string.printable on my machine contains:

0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~ \t\n\r\x0b\x0c

EDIT: On Python 3, filter will return an iterable. The correct way to obtain a string back would be:

''.join(filter(lambda x: x in printable, s))

An easy way to change to a different codec, is by using encode() or decode(). In your case, you want to convert to ASCII and ignore all symbols that are not supported. For example, the Swedish letter å is not an ASCII character:

    >>>s = u'Good bye in Swedish is Hej d\xe5'
    >>>s = s.encode('ascii',errors='ignore')
    >>>print s
    Good bye in Swedish is Hej d

Edit:

Python3: str -> bytes -> str

>>>"Hej då".encode("ascii", errors="ignore").decode()
'hej d'

Python2: unicode -> str -> unicode

>>> u"hej då".encode("ascii", errors="ignore").decode()
u'hej d'

Python2: str -> unicode -> str (decode and encode in reverse order)

>>> "hej d\xe5".decode("ascii", errors="ignore").encode()
'hej d'

According to @artfulrobot, this should be faster than filter and lambda:

re.sub(r'[^\x00-\x7f]',r'', your-non-ascii-string) 

See more examples here Replace non-ASCII characters with a single space

Your question is ambiguous; the first two sentences taken together imply that you believe that space and “period” are non-ASCII characters. This is incorrect. All chars such that ord(char) <= 127 are ASCII characters. For example, your function excludes these characters !”#$%&\'()*+,-./ but includes several others e.g. []{}.

Please step back, think a bit, and edit your question to tell us what you are trying to do, without mentioning the word ASCII, and why you think that chars such that ord(char) >= 128 are ignorable. Also: which version of Python? What is the encoding of your input data?

Please note that your code reads the whole input file as a single string, and your comment (“great solution”) to another answer implies that you don’t care about newlines in your data. If your file contains two lines like this:

this is line 1
this is line 2

the result would be 'this is line 1this is line 2' … is that what you really want?

A greater solution would include:

1. a better name for the filter function than onlyascii

2. recognition that a filter function merely needs to return a truthy value if the argument is to be retained:

   def filter_func(char):
       return char == '\n' or 32 <= ord(char) <= 126
   # and later:
   filtered_data = filter(filter_func, data).lower()
   

You may use the following code to remove non-English letters:

import re
str = "123456790 ABC#%? .(朱惠英)"
result = re.sub(r'[^\x00-\x7f]',r'', str)
print(result)

This will return

123456790 ABC#%? .()

If you want printable ascii characters you probably should correct your code to:

if ord(char) < 32 or ord(char) > 126: return ''

this is equivalent, to string.printable (answer from @jterrace), except for the absence of returns and tabs (‘\t’,’\n’,’\x0b’,’\x0c’ and ‘\r’) but doesnt correspond to the range on your question

Working my way through Fluent Python (Ramalho) – highly recommended. List comprehension one-ish-liners inspired by Chapter 2:

onlyascii = ''.join([s for s in data if ord(s) < 127])
onlymatch = ''.join([s for s in data if s in
              'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'])