How can I remove non-ASCII characters but leave periods and spaces?

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

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()
   

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 dxe5'
    >>>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 dxe5".decode("ascii", errors="ignore").encode()
'hej d'

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

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

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

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'])

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#%? .()

this is best way to get ascii characters and clean code, Checks for all possible errors

from string import printable

def getOnlyCharacters(texts):
    _type = None
    result = ''
    
    if type(texts).__name__ == 'bytes':
        _type = 'bytes'
        texts = texts.decode('utf-8','ignore')
    else:
        _type = 'str'
        texts = bytes(texts, 'utf-8').decode('utf-8', 'ignore')

    texts = str(texts)
    for text in texts:
        if text in printable:
            result += text
            
    if _type == 'bytes':
        result = result.encode('utf-8')

    return result

text = '�Ahm�����ed Sheri��'
result = getOnlyCharacters(text)

print(result)
#input --> �Ahm�����ed Sheri��
#output --> Ahmed Sheri