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→INVESTIGATION 1: Advanced String Formatting
= INVESTIGATION 1: Advanced String Formatting =
== PART 2 1 - String Formatting Basic Fundamentals==
:In Python scripting, using plus signs and commas for string concatenation is very limited and can become messy when when used at length with many values and/or calculations. This section will cover the '''format()''' function that can be used with every type of string. This function allows the user of Python to create well formatted code, to align text, and to convert values efficiently and cleanly. While this section uses lists and dictionaries, they contain strings which can be accessed and displayed in a formatted manner.
print('{City} {Province} {Country}'.format(City='Toronto', Province='ON', Country='Canada'))
</source>
== PART 2 - String Formatting Advanced Features ==
This section shows you how to perform more advanced formatting features via the '''format()''' function. You will learn how to format numbers and aligning strings (text).
:'''Perform the Following Steps'''
:#Make certain you are still in your ipython3 shell.<br><br>Let's start advanced formatting for '''numbers'''. Try issuing content below in order to observe the various ways to change the output inside the curly brace '''{}''' while formatting. This formatting change is done by placing a colon inside the curly braces, following by a letter '''{0:f}'''<br><br>
:#Issue the following:<source>
number1 = 50
number2 = -50
number3 = 1.50
print('{0:f}'.format(number1)) # "0" is the position just like other format() functions
print('{0:f}'.format(number2)) # A colon separate the position/index areas from the extra functionality
print('{0:f}'.format(number3)) # "f" represents the fixed point number
</source>Notice that there are many decimal places after this number. This makes the number look "ugly". We need to further format the number to indicate the number of decimal places (or no decimal places if number is an integer). A fixed point number means that it can control the number of digits that come after the decimal point, try changing the '''.2''' to any other number and experiment.<br><br>
:#Issue the following to demonstrate:<source>
print('{0:.0f}'.format(number1)) # Show no digits after decimal point
print('{0:.2f}'.format(number2)) # Show two digits after decimal point
print('{0:.1f}'.format(number3)) # Show one digit after decimal point
</source>
:#Numbers can be displayed with the '''-''' or '''+''' signs before the digits, this could be important in formatting. Issue the following to demonstrate:<source>
print('{0: f}'.format(number1)) # Show a space where plus sign should be
print('{0: f}'.format(number2)) # Shows negative sign normally
print('{0: f}\n{1: f}'.format(number1, number2)) # The space before the f lines up positive and negative numbers
</source>
:#Placing a '''+''' before the f changes the format so that plus signs show up for positive numbers and negative signs show up for negative numbers. Try issuing the following:<source>
print('{0:+f}'.format(number1)) # Show a space where plus sign should be
print('{0:+f}'.format(number2)) # Shows negative sign normally
print('{0:+f}\n{1:+f}'.format(number1, number2)) # The space before the f lines up positive and negative numbers
</source>
:#Combining fixed point positions can be performed by issuing the following:<source>
print('{0:+.2f}'.format(number1))
print('{0:+.2f}'.format(number2))
print('{0:+.2f}\n{1:+.2f}'.format(number1, number2))
</source>In the event that the numbers being shown are all integers and do no require the decimal values, instead of using '''{:f}''',<br> use '''{:d}''' for decimal '''integers'''.<br><br>
:#To demonstrate, issue the following:<source>
print('{0:d}'.format(number1))
print('{0:d}'.format(number2))
print('{0: d}'.format(number1))
print('{0: d}'.format(number2))
print('{0:+d}'.format(number1))
print('{0:+d}'.format(number2))
</source>'''NOTE:''' When using '''{:d}''' be careful not to use numbers with a decimal value in them, the following will create a error<br><br>
:#Issue the following to see the difference:<source>
number3 = 1.50
print('{0:d}'.format(number3))
</source>Next, let's move on to aligning '''strings''' (text). This is the process of adding padding to the left of our text, the right of our text, or aligning to the centre or our text (i.e. padding both left and right). Through the alignment the text field size, any string can be set to allow it to fit within a column (or columns), and make it easier for the user to read data.<br><br>
:#Start by using a string but placeing a number value after the colon '''{0:10}''' by issuing:<source>
string1 = 'hello'
string2 = 'world'
print('{0:10}{1}'.format(string1, string2)) # Make sure string1 is 10 characters aligned to the left
print('{0:6}{1}'.format(string1, string2)) # Make sure string1 is 6 characters aligned to the left
</source>By default, the format() function aligns to the left, the symbol to do this is '''<''' which is a shortcut for : '''{0:<10}''' when used in the curely braces. Now whenever a different string is placed inside it always aligns to the left 10 characters. This allows for concise code to generate well structured output<br><br>
:#To demonstrate this, issue the following:<source>
# Without positional argument numbers
print('{:<10} {:<10} {:<10}\n{:<10} {:<10} {:<10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123'))
# With positional argument numbers
print('{0:<10} {1:<10} {2:<10}\n{3:<10} {4:<10} {5:<10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123'))
</source>
:#Next try using right alignment with the '''>''' symbol replacing the left alignment<source>
# Without positional argument numbers
print('{:>10} {:>10} {:>10}\n{:>10} {:>10} {:>10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123'))
# With positional argument numbers
print('{0:>10} {1:>10} {2:>10}\n{3:>10} {4:>10} {5:>10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123'))
</source>
:#Finally, you can centre the alignment of strings using the '''^''' symbol. Issue the following:<source>
# Without positional argument numbers
print('{:^10} {:^10} {:^10}\n{:^10} {:^10} {:^10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123'))
# With positional argument numbers
print('{0:^10} {1:^10} {2:^10}\n{3:^10} {4:^10} {5:^10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123'))
</source>The alignment character can be changed to any other character that is wanted for the output. By default it's a space, but it could be anything else by adding an additional character '''{:M<10}''' such as '''M''' or '''*''' before the alignment character<br><br>
:#To see this, issue the following:<source>
print('{:*^10} {:*^10} {:*^10}\n{:*^10} {:*^10} {:*^10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123')) # Without positional argument numbers
print('{:.^10} {:.^10} {:.^10}\n{:.^10} {:.^10} {:.^10}'.format('abc', 'def', 'ghi', 'jkl123', 'mno123', 'pqr123')) # Without positional argument numbers
</source>You can make the output appear better by creating borders. Below is a function in order to create a border containing data. If you learned MySQL, you may have seen borders used to display table data, etc. Try defining and running the user-defined function below to see what happens.<br><br>
:#Issue the following:<source>
# Define the function "print_with_borders()":
def print_with_borders():
print('|{:-^10}|'.format('nums'))
print('|{:^5}{:^5}|'.format(1,2))
print('|{:^5}{:^5}|'.format(3,4))
print('|{}|'.format('-'*10))
# Run the function "print_with_borders()":
print_with_borders()
</source>
'''Create a Script Demonstrating Formatting Strings'''
:'''Perform the Following Instructions:'''
::#Create the '''~/ops435/lab4/lab4e.py''' script. The purpose of this script is to demonstrate formatting string output from a large data structure.
::#Use the following template to get started:<source>
#!/usr/bin/env python3
# Formatted Strings
dict_york = {'Address': '70 The Pond Rd', 'City': 'Toronto', 'Country': 'Canada', 'Postal Code': 'M3J3M6', 'Province': 'ON'}
college = 'Seneca College'
def print_college_address():
# Prints out the keys and values from the dictionary
# Formats the output to have a title bar with a title
# EXACT SAME output as the samples
if __name__ == '__main__':
print_college_address(dict_york, college)
</source>
:::*The '''print_college_address()''' function does NOT return anything
:::*The '''print_college_address()''' function accept two arguments
:::*The first argument is a '''dictionary'''
:::*The second argument is a '''string'''
:::*The title printed is '''center''' aligned by '''40 characters''' using '-' instead of space for alignment
:::*The keys printed are '''center''' aligned by '''20 characters'''
:::*The values printed are '''center''' aligned by '''20 characters'''
:::*The output must match the sample output EXACTLY if one character is off it will be wrong
:::'''Sample Run 1:'''<source>
run lab4e.py
|-------------Seneca College-------------|
| Address 70 The Pond Rd |
| Province ON |
| Postal Code M3J3M6 |
| City Toronto |
| Country Canada |
|----------------------------------------|
</source>
:::'''Sample Run 2(with import):'''<source>
import lab4e
dict_york = {'Address': '70 The Pond Rd', 'City': 'Toronto', 'Country': 'Canada', 'Postal Code': 'M3J3M6', 'Province': 'ON'}
dict_newnham = {'Address': '1750 Finch Ave E', 'City': 'Toronto', 'Country': 'Canada', 'Postal Code': 'M2J2X5', 'Province': 'ON'}
college = 'Seneca College'
lab4e.print_college_address(dict_york, college)
|-------------Seneca College-------------|
| Address 70 The Pond Rd |
| Province ON |
| Postal Code M3J3M6 |
| City Toronto |
| Country Canada |
|----------------------------------------|
lab4e.print_college_address(dict_newnham, college)
|-------------Seneca College-------------|
| Address 1750 Finch Ave E |
| Province ON |
| Postal Code M2J2X5 |
| City Toronto |
| Country Canada |
|----------------------------------------|
</source>
::3. Exit the ipython3 shell, download the checking script and check your work. Enter the following commands from the bash shell.<source>
cd ~/ops435/lab4/
pwd #confirm that you are in the right directory
ls CheckLab4.py || wget matrix.senecac.on.ca/~acoatley-willis/CheckLab4.py
python3 ./CheckLab4.py -f -v lab4e
</source>
::4. Before proceeding, make certain that you identify any and all errors in lab4e.py. When the checking script tells you everything is OK before proceeding to the next step.
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