02 Prove: Calling Functions

Helpful Documentation

• The preparation content for this lesson explains how to call a function and a method.

• The datetime.now() method from the standard Python datetime module will get the current date and time from your computer’s operating system. Here is an excerpt from the official reference for the datetime.now method:

  datetime.now(tz=None)

  Return the current local date and time.

  tz is optional, but if it is not None, it must be a tzinfo (time zone information) object

  These two Microsoft videos explain how to use methods from the standard datetime module.

  • Date data types (8 minutes)
  • Demonstration: Dates (9 minutes)

  The following Python code imports the datetime class from the datetime module and calls the datetime.now method to get the current date and time from a computer’s operating system. Then it uses an f-string to format and print the current date.

  # Import the datetime class from the datetime
  # module so that it can be used in this program.
  from datetime import datetime
  
  # Call the now() method to get the current
  # date and time as a datetime object from
  # the computer's operating system.
  current_date_and_time = datetime.now()
  
  # Use an f-string to print only the date
  # part of the current date and time.
  print(f"{current_date_and_time:%Y-%m-%d}")

  > python date_example.py
  2020-07-24

  After the computer executes line 8 in the above code, the variable current_date_and_time will hold the current date and time. Within the f-string at line 12, the string sequences that begin with the percent symbol (%) are called format codes. The format codes and their meaning are listed in the official Python datetime reference. As shown in the terminal window above, the previous example code will print the current date and time to the terminal window with four digits for the year, two digits for the month, and two digits for the day of the month.

• The built-in open() function opens a file for reading or writing. Here is an excerpt from the official documentation for the open function:

  open(filename, mode="rt")

  Open a file and return a corresponding file object.

  filename is the name of the file to be opened.

  mode is an optional string that specifies the mode in which the file will be opened. It defaults to "rt" which means open for reading in text mode. Other common values are "wt" for writing a text file (truncating the file if it already exists), and "at" for appending to the end of a text file that already exists (and creating and writing to a text file that doesn’t exist).

• The built-in print() function prints text to a terminal window or to a text file. Here is an excerpt from the official documentation for the print function:

  print(*objects, sep=" ", end="\n", file=sys.stdout, flush=False)

  Print objects to the text stream file, separated by sep and followed by end. sep, end, file and flush, if present, must be given as named arguments.

• You may want to review the lesson 11 preparation content from CSE 110 which includes several examples for opening and reading from a text file.

  The following example code calls the open function at line 6 to open a file named cities.txt for appending text ("at"). The code then calls the print function two times at lines 9 and 10 to print two lines of text to the cities.txt file.

  city_name = "Accra"
  elevation = 61
  population = 4200000
  
  # Open a text file named cities.txt in append mode.
  with open("cities.txt", "at") as cities_file:
  
      # Print a city's name and information to the file.
      print(city_name, file=cities_file)
      print(f"{elevation}, {population}", file=cities_file)

  Notice in the previous example at line 6 that the call to the open function is inside a with statement. Opening a file in a with statement, ensures that the computer will automatically close the file when the computer finishes executing the code inside the with block.

  The variable cities_file, which is created at line 6, is a reference to the open cities.txt file. At both lines lines 9 and 10, the cities_file is a named argument that causes the print function to print to the cities.txt file instead of printing to the terminal window.

Help from an AI Tutor

You could use a generative AI as a tutor to help you write and troubleshoot your program. Bro. Lee Barney created a custom Chat GPT named Pythonista that is designed to focus on Python functions, loops, if statements, and related programming concepts. If your program is generating an error, ask Pythonista a question like this:

I'm writing a Python program that computes the approximate volume of air in a tire. When I run my program, it causes the following error. Please suggest some mistakes that might cause this error.

(Copy and paste the error message here.)

You could also ask Pythonista a question about one of your functions, like this:

I wrote the following Python function that is supposed to (type a short description here). However, the function isn't (type what it's not doing correctly here). Please help me fix this function.

(Copy and paste your Python function here.)

Help from a Human Tutor

As a BYU-Idaho campus or online student you can get help from a tutor to complete your CSE 111 assignments. Each tutor is a current BYU-Idaho student employed by BYU-Idaho. Meeting with a tutor is free. It will not cost you any money to meet with a tutor. To get help from a tutor, you simply make an appointment and then meet with the tutor. Campus students meet with tutors in the tutoring center. Online students meet with tutors in Zoom. To make an appointment, follow the instructions in the course tutoring guide.