def for_value(prompt_text,
convert=(lambda x: x),
is_legal=(lambda x: True),
default=None,
error_message='reenter'):
"""
Prompt for value using the specified prompt_text (with default in brackets
appended if it is non-None) followed by ': '; convert the entered value
(or use the default if the user just presses enter), ensure is_legal
returns True when called on it, and return that value.
Display error_messages for all possible failures
See the comments in the code for more details
See the calls to for_value below, for examples of how it is called.
"""
while True:
try:
# display answer (and default, if supplied) and ': '; read str that is user's answer
response = input(prompt_text + ('[' + str(default) +
']' if default != None else '') +
': ')
# if there is no answer, and no default, print error message and reprompt
# kludge: so the user cannot enter an empty string unless the empty string is a default!
if len(response) == 0 and default == None:
print(
leading(prompt_text, extra=2) +
'Must enter a value: there is no default')
continue
# set answer to either be the default (if there is no answer) or convert the user's answer
# see except clause, in case conversion fails: e.g., int('abc') throws an exception
answer = default if len(
response) == 0 and default != None else convert(response)
# if the answer (default or user's) is legal, return it, other print the error message
if is_legal(answer):
return answer
else:
print(
leading(prompt_text, extra=2) + 'Entry Error:',
"'" + str(answer) + "'; ", error_message)
# if conversion raises an exception, print an error message and reprompt
except Exception as x:
print(leading(prompt_text, extra=2) + 'Exception:', x)
print(leading(prompt_text, extra=2) +
'Possible error: cannot convert str \'',
response,
'\' to specified type of value',
sep='')
def for_int_between(prompt_text, low, high, default=None, error_message=''):
lead = leading(prompt_text, extra=2)
return for_value(
prompt_text + '(' + str(low) + '..' + str(high) + ')', int,
(lambda x: type(x) is int and low <= x <= high), default,
error_message + '\n' + lead + 'Please enter a value in the range [' +
str(low) + ',' + str(high) + ']')
"""
def for_char(
prompt_text,
default=None,
legal=None,
error_message='Please enter one char in the range (if specified)'):
lead = leading(prompt_text, extra=2)
return for_value(
prompt_text + ('(' + legal + ')' if legal != None else ''),
(lambda x: x[0]), (lambda x: x in legal) if legal != None else
(lambda x: True), default,
error_message + ('\n' + lead + 'Please enter one of ' +
legal if legal != None else ''))
"""
def for_float(prompt_text,
default=None,
is_legal=(lambda x: True),
error_message='not a legal value'):
"""
Prompt for a float; use the specified prompt_text (with default in brackets
appended if it is non-None) followed by ': '; verify that the entered value
(using default if the user just presses enter) is a float and is_legal
returns True when called on it (and if not display the error_message)
See the call to for_value below, and the documentation and code for for_value above.
"""
lead = leading(prompt_text, extra=2)
return for_value(
prompt_text, float, (lambda x: type(x) is float and is_legal(x)),
default, error_message + ':\n' + lead + 'Please enter a legal value')
def for_string(prompt_text,
default=None,
is_legal=(lambda x: True),
error_message=''):
"""
Prompt for a string; use the specified prompt_text (with default in brackets
appended if it is non-None) followed by ': '; verify that the entered value
(using default if the user just presses enter) returns True when is_legal is
called on it (and if not display the error_message)
See the call to for_value below, and the documentation and code for for_value above.
"""
lead = leading(prompt_text, extra=2)
return for_value(
prompt_text, (lambda x: x), is_legal, default,
error_message + '\n' + lead + 'Please enter a legal String')