Regarding string methods

Question

I'm currently working through Automate the Boring Stuff with Python book and run into curious issue on chapter 7. When trying to execute the following code:

def isPhoneNumber(text):
 if len(text) != 12:
 return False
 for i in range(0, 3):
 if not text[i].isdecimal():
 return False
 if text[3] != "-":
 return False
 for i in range(4, 7):
 if not text(i).isdecimal():
 return False
 if text[7] != "-":
 return False
 for i in range(8, 12):
 if not text[i].isdecimal():
 return False
 return True
print("415-555-4242 is a phone number:")
print(isPhoneNumber("415-555-4242"))
print("Moshi moshi is a phone number:")
print(isPhoneNumber("Moshi moshi"))

I get the following error message:

Traceback (most recent call last):
 File "automation.py", line 27, in <module>
 print(isPhoneNumber("415-555-4242"))
 File "automation.py", line 13, in isPhoneNumber
 if not text(i).isdecimal():
TypeError: 'str' object is not callable

Switching the str.isdecimal() method for str.isdigit() method allows me to execute the code properly, but I would like to know why the isdecimal() method will not work?

• Eli Korvigo: If your book teaches you this sort of Python, then you'd better find another one. The code is very unpythonic.
• Roland Smith: As @EliKorvigo says, this would be an excellent use case for regular expressions. The regular expression '\d{3}-\d{3}-\d{4}' matches your kind of phone numbers.
• Terry Jan Reedy: text(i).isdigit() would raise the same error. You must have fixed the () typo at the same time.
• DYZ: @EliKorvigo: Do not blame the book. All CS1-level books in Python follow this approach. Regular expressions are extremely hard to grasp for those who are taking their first programming course.
• Eli Korvigo: @DYZ I'm more concerned about this iteration style.

Answer 1

The error has nothing to do with isdecimal(). You have a typo in how you extract the character from text. The

if not text(i).isdecimal():

should read

if not text[i].isdecimal():

(note the square brackets.)

• Terry Jan Reedy: I am not the downvoter, but perhaps, guessing, he thought that this answer should instead have been a comment, coupled with a vote to close as off-topic because just a typo.
• Pekka Pousi: @NPE Thank you! Should have paid more attention for possible typos.

Answer 2

 File "automation.py", line 13, in isPhoneNumber
 if not text(i).isdecimal():
TypeError: 'str' object is not callable

The typeError is on line 13, where you are calling a string object. Use [] not ()