Introduction to Python

About these Notes

These are the introductory concepts to the programming language python. In these notes there will be concepts that the PCDE course by MIT xPRO addressed.

Data Types

All variables in python are dynamic, but python does offer some primitives. There's int, bool, float, and str operates in a kind of fuzzy area.

It's possible to cast these into each other using their constructors. For example:

a = 3
b = str(a)
c = 7.4
d = int(c)
print(a) # Prints a number 3
print(b) # Prints a string, 3 as it's casted to a str
print(c) # Prints a float 7.4
print(d) # Prints an int casted float,
# ie it will round down to nearest int

Bools

Boolean, or bool values are any True or False value. The values True or False lead to a variable to become a bool type when they're assigned. This is also true for boolean expressions.

print(True + True + False) # prints '2'

The above expression prints out the number 2. This is because True gets cast to 1 and then 1 plus 1 is 2. The False becomes 0 so doesn't affect the sum.

Boolean Expressions

Boolean results follow basic logical expressions as return values. These expressions include:

Ints

Integers, or ints are primitive types that express only whole numbers. It's possible to assign variables to literal ints. It involves typing any number after assignment with no decimal point. To cast an int simply invoke its constructor int() on a variable or literal. This works on floats and even booleans, but booleans become 1 or 0.

Floats

Floats, or float are floating point numbers, that can take really small fractional values or really large values by expressing numbers akin to scientific notation with exponents and decimals.

It's posisible to cast floats from ints using the float() constructor. The decimal value gets assumed to be 0. When casting from bool values to float a variable becomes 1.0 or 0.0. This also applies to when using numeric operators like + or - on bools.

Number literals with a decimal point get cast to floats automatically.

Strings

Strings are a bit different. They get treated as both primitives like the previous types. They also get treated like collections which will get covered later. But most importantly, they get access to some operators found only with collection objects like lists.

Template strings are possible to cast variables into strings. Just use f"({x}, {y})" to represent the variables x = 2 y = 3 as (2, 3).

Raw strings are another kind of special string template literal. Any string beginning with r becomes raw strings where everything parses. The string r"blah\n\\" doesn't omit the escape characters.

Replace

Using the s.replace(old_str, new_str, count) function replaces specified occurrences of the string of the method call with another; in this case new_str replaces old_str in the string s. The count parameter specifies optionally how many occurrences of the old value to replace, it defaults to all.

Case Transform

The swapcase() method for strings replaces all lower case with upper case letters and vice-versa. The upper() method of strings will change a string to all uppercase. And lower() does the same, but lowercase.

Accessing and Slicing Strings

Strings can use bracket operators [ & ] are usable on strings. This means [index] can access single characters in a string by its index. Also string slices are accessible using bracket slice operators. A start, stop, step parameter gets used like string[start:stop:step] to grab a slice of the string.

Please note, the stop parameter is exclusive, thus the value before that index is the last item in the slice. Also, the step parameter defaults to 1 when not included.

Operators

Arithmetic Operators

Python arithmetic operators follow the standard order of operations. Below are all the valid binary arithmetic operators available.

Strings can use the + operator to concatenate strings. The * operator used on a string concatenates the string many times.

Collections

Covered in detail in the python collection notes.

References

• Floating Point Architecture (by Wikipedia, the free encyclopedia)
• Floor and Ceiling Functions (by Wikipedia, the free encyclopedia)

Note Links

• Python Overview Notes
• Professional Certification of Data Enginering by MIT xPRO Course Overview (Backlink)
• Python Collections
• Modulo Operation (by Wikipedia, the free encyclopedia)