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Using Datetime for user input

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flebber

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Using Datetime for user input

Sep 25th, 2009

Hi

I want to prompt the user to enter the date dd/mm/year and use this later as part of filename and later as object in file(if this helps searching). Does using datetime ensure that user input will be a valid input? I would like the output to be year-mm-dd

My below version errors.

#This doesn't error but also doesn't prompt me for input.

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
from datetime import date
def ObtainDate():
   input = raw_input("Type Date dd/mm/year: ")
   d = datetime.strptime(input, "%y-%m-%d")
print ObtainDate
from datetime import date
def ObtainDate():
   input = raw_input("Type Date dd/mm/year: ")
   d = datetime.strptime(input, "%y-%m-%d")
print ObtainDate

Last edited by flebber; Sep 25th, 2009 at 9:02 pm.

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Re: Using Datetime for user input

Sep 25th, 2009

Firstly 'input' is a reserved word in python, it's used to get input from the user, (rather like raw_input!). So that's why this line of code fails to do anything:

 Help with Code Tags 
 PYTHON Syntax (Toggle Plain Text) 
input = raw_input("Type Date dd/mm/year: ")
input = raw_input("Type Date dd/mm/year: ")

Change your variable 'input' to something like 'userInput' or just anything that isn't a reserved word and you will get your prompt!

Secondly...No I don't think that strptime will work used like that! if your users enter anything other than yy-mm-dd, it will bomb out with an error!
But if you use a try: except: block inside a loop, you should be able to get the user to repeatedly enter the date until the format is correct!

Check this out:

 Help with Code Tags 
 PYTHON Syntax (Toggle Plain Text) 
import datetime
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d = datetime.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
        except:
            print "Doh, try again!\n"
    return d
 
#test the function
print ObtainDate()
import datetime
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d = datetime.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
        except:
            print "Doh, try again!\n"
    return d

#test the function
print ObtainDate()

I've not done any exception handling code for a while, but there should be a way of outputting to the user the reason that the exception occurred.

I'll leave that up to you to look up!

Cheers for now,
Jas

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Those who understand binary .....
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flebber

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Re: Using Datetime for user input

Sep 26th, 2009

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Originally Posted by JasonHippy

Firstly 'input' is a reserved word in python, it's used to get input from the user, (rather like raw_input!). So that's why this line of code fails to do anything:
Help with Code Tags

PYTHON Syntax (Toggle Plain Text)
input = raw_input("Type Date dd/mm/year: ")
input = raw_input("Type Date dd/mm/year: ")
Change your variable 'input' to something like 'userInput' or just anything that isn't a reserved word and you will get your prompt!

Secondly...No I don't think that strptime will work used like that! if your users enter anything other than yy-mm-dd, it will bomb out with an error!
But if you use a try: except: block inside a loop, you should be able to get the user to repeatedly enter the date until the format is correct!

Check this out:
Help with Code Tags

PYTHON Syntax (Toggle Plain Text)
import datetime
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d = datetime.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
        except:
            print "Doh, try again!\n"
    return d
 
#test the function
print ObtainDate()
import datetime def ObtainDate(): isValid=False while not isValid: userIn = raw_input("Type Date dd/mm/yy: ") try: # strptime throws an exception if the input doesn't match the pattern d = datetime.datetime.strptime(userIn, "%d/%m/%y") isValid=True except: print "Doh, try again!\n" return d #test the function print ObtainDate()
I've not done any exception handling code for a while, but there should be a way of outputting to the user the reason that the exception occurred.

I'll leave that up to you to look up!

Cheers for now,
Jas

Awesome I like it just one question why does the line below have datetime twice?

d = datetime.datetime.strptime(userIn, "%d/%m/%y")

I think with exception handling that getting the user a reason as to why input was wrong could use the try: obj.method but I will need to look into this further.

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Re: Using Datetime for user input

Sep 26th, 2009

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Originally Posted by flebber

Awesome I like it just one question why does the line below have datetime twice?

d = datetime.datetime.strptime(userIn, "%d/%m/%y")

It's the only way I could access the strptime function.
The first datetime refers to the datetime package, the second refers to the datetime class.

In my import I could have used something like:

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PYTHON Syntax (Toggle Plain Text)

import datetime as dt

This gives the datetime package an alias (dt). So to call the strptime function I'd need to use:

 Help with Code Tags 
 PYTHON Syntax (Toggle Plain Text) 
dt.datetime.strptime(userInput, pattern)
dt.datetime.strptime(userInput, pattern)

So my strptime function call breaks into the following parts:
packageName.className.function(parameter1, parameter2)
or:
datetime.datetime.strptime(userInput, "%d/%m/%y")

Hope that clarifies things for you!

Cheers for now,
Jas.

Last edited by JasonHippy; Sep 26th, 2009 at 8:22 am.

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Re: Using Datetime for user input

Sep 26th, 2009

To find the error class simply create the error ...

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
import datetime as dt
 
# the date has to be entered in dd/mm/yy format
# entering dd/mm/yyyy by mistake will create an error
# the error class will be --> ValueError
test_date = "15/07/2003"
 
d1 = dt.datetime.strptime(test_date, "%d/%m/%y")
import datetime as dt

# the date has to be entered in dd/mm/yy format
# entering dd/mm/yyyy by mistake will create an error
# the error class will be --> ValueError
test_date = "15/07/2003"

d1 = dt.datetime.strptime(test_date, "%d/%m/%y")

Also be aware that d1 will be a datetime object and not a string, so you have to do some simple extra coding ...

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
import datetime as dt
 
# date has been entered in dd/mm/yy format
test_date = "15/07/03"
 
d1 = dt.datetime.strptime(test_date, "%d/%m/%y")
 
print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>
 
# convert datetime object to a 10 character string
d2 = str(d1)[:10]
 
print d2, type(d2)  # 2003-07-15 <type 'str'>
 
# now you can use string d2 to create filenames
fname = "data.dat"
new_fname = d2 + fname
 
print new_fname  # 2003-07-15data.dat
import datetime as dt

# date has been entered in dd/mm/yy format
test_date = "15/07/03"

d1 = dt.datetime.strptime(test_date, "%d/%m/%y")

print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>

# convert datetime object to a 10 character string
d2 = str(d1)[:10]

print d2, type(d2)  # 2003-07-15 <type 'str'>

# now you can use string d2 to create filenames
fname = "data.dat"
new_fname = d2 + fname

print new_fname  # 2003-07-15data.dat

This file name should sort well.

Last edited by vegaseat; Sep 26th, 2009 at 10:04 am.

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flebber

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Re: Using Datetime for user input

Sep 26th, 2009

I really like it a lot, and it works well

thanks jasonHippy and Vegaseat. The only thing I am going to look into when I am not so tired is that if you supply a correctly formatted date but say you use the 31st September as 31/09/09 which doesn't exist it errors "Try again! dd/mm/yy" intimating its a format error when its a date doesn't exist error.

Which simply means I need to catch 2 errors.

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
mport datetime as dt
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d1 = dt.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
#Perhaps set another try here.
            print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>
            "convert datetime object to a 10 character string"
            d2 = str(d1)[:10]
            print d2, type(d2)  # 2003-07-15 <type 'str'>
        except:
            print "Try again! dd/mm/yy\n"
    Fname = "data.dat"
    newFname = d2 + Fname
    return newFname
print ObtainDate()  # 2003-07-15data.dat
mport datetime as dt
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d1 = dt.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
#Perhaps set another try here.
            print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>
            "convert datetime object to a 10 character string"
            d2 = str(d1)[:10]
            print d2, type(d2)  # 2003-07-15 <type 'str'>
        except:
            print "Try again! dd/mm/yy\n"
    Fname = "data.dat"
    newFname = d2 + Fname
    return newFname
print ObtainDate()  # 2003-07-15data.dat

Last edited by flebber; Sep 26th, 2009 at 12:37 pm. Reason: tired

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Re: Using Datetime for user input

Sep 26th, 2009

You can trap error details this way:

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
import datetime as dt
 
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d1 = dt.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
#Perhaps set another try here.
            print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>
            "convert datetime object to a 10 character string"
            d2 = str(d1)[:10]
            print d2, type(d2)  # 2003-07-15 <type 'str'>
        except ValueError, what_error:
            print what_error
            print "Try again! dd/mm/yy\n"
    Fname = "data.dat"
    newFname = d2 + Fname
    return newFname
 
print ObtainDate()  # 2003-07-15data.dat
import datetime as dt

def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d1 = dt.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
#Perhaps set another try here.
            print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>
            "convert datetime object to a 10 character string"
            d2 = str(d1)[:10]
            print d2, type(d2)  # 2003-07-15 <type 'str'>
        except ValueError, what_error:
            print what_error
            print "Try again! dd/mm/yy\n"
    Fname = "data.dat"
    newFname = d2 + Fname
    return newFname

print ObtainDate()  # 2003-07-15data.dat

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flebber

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Re: Using Datetime for user input

Sep 26th, 2009

•

Originally Posted by Ene Uran

You can trap error details this way:
Help with Code Tags

python Syntax (Toggle Plain Text)
import datetime as dt
 
def ObtainDate():
    isValid=False
    while not isValid:
        userIn = raw_input("Type Date dd/mm/yy: ")
        try: # strptime throws an exception if the input doesn't match the pattern
            d1 = dt.datetime.strptime(userIn, "%d/%m/%y")
            isValid=True
#Perhaps set another try here.
            print d1, type(d1)  # 2003-07-15 00:00:00 <type 'datetime.datetime'>
            "convert datetime object to a 10 character string"
            d2 = str(d1)[:10]
            print d2, type(d2)  # 2003-07-15 <type 'str'>
        except ValueError, what_error:
            print what_error
            print "Try again! dd/mm/yy\n"
    Fname = "data.dat"
    newFname = d2 + Fname
    return newFname
 
print ObtainDate()  # 2003-07-15data.dat
import datetime as dt def ObtainDate(): isValid=False while not isValid: userIn = raw_input("Type Date dd/mm/yy: ") try: # strptime throws an exception if the input doesn't match the pattern d1 = dt.datetime.strptime(userIn, "%d/%m/%y") isValid=True #Perhaps set another try here. print d1, type(d1) # 2003-07-15 00:00:00 <type 'datetime.datetime'> "convert datetime object to a 10 character string" d2 = str(d1)[:10] print d2, type(d2) # 2003-07-15 <type 'str'> except ValueError, what_error: print what_error print "Try again! dd/mm/yy\n" Fname = "data.dat" newFname = d2 + Fname return newFname print ObtainDate() # 2003-07-15data.dat

Much neater than a nested exception