Python. Part 2. Functions & Packages

Function is a piece of reusable code, aimed at solving a particular task. Call Function instead of writing code yourself.

Function max shows in output the maximum number from the list 'fam' -> max(fam)

Assign a function to the variable: tallest = max(fam)

Function round():

round(1.68, 1) -> output 1.7 
round(1.68) -> output 2

Get more info on function in Python: help(round) or ?round

Built-in functions in Python

Exercise 1

# Create variables var1 and var2
var1 = [1, 2, 3, 4]
var2 = True

# Print out type of var1
print(type(var1))

# Print out length of var1
print(len(var1))

# Convert var2 to an integer: out2
out2 = int(var2)
print(out2)

<script.py> output:
    <class 'list'>
    4
    1

Functions with multiple arguments

Exercise 2

# Create lists first and second
first = [11.25, 18.0, 20.0]
second = [10.75, 9.50]

# Paste together first and second: full
full = first + second

# Sort full in descending order: full_sorted
full_sorted = sorted(full, reverse=True)

# Print out full_sorted
print (full_sorted)

<script.py> output:
    [20.0, 18.0, 11.25, 10.75, 9.5]

Additional information: Sorting Techniques in Python

Methods

In Python, everything is an object.

• There are different functions in Python, like type, max and round.

• Methods are functions that are specific to Python objects.

• Depending on the type of an object (string, int, etc), methods behave differently.

• Some methods can change the objects they are called on.

    # string to experiment with: place
    place = "poolhouse"
  
    # Use upper() on place
    place_up = place.upper()
  
    # Print out place and place_up
    print(place)
    print(place_up)
  
    # Print out the number of o's in place
    place_count = place.count('o')
    print(place_count)
  
    <script.py> output:
        poolhouse
        POOLHOUSE
        3
  

# Create list areas
areas = [11.25, 18.0, 20.0, 10.75, 9.50]

# Print out the index of the element 20.0
print(areas.index(20.0))

# Print out how often 9.50 appears in areas
print(areas.count(9.5))

<script.py> output:
    2
    1

# Create list areas
areas = [11.25, 18.0, 20.0, 10.75, 9.50]

# Use append twice to add poolhouse and garage size
areas.append(24.5)
areas.append(15.45)

# Print out areas
print(areas)

# Reverse the orders of the elements in areas
areas.reverse()

# Print out areas
print(areas)

<script.py> output:
    [11.25, 18.0, 20.0, 10.75, 9.5, 24.5, 15.45]
    [15.45, 24.5, 9.5, 10.75, 20.0, 18.0, 11.25]

Strings (str) public methodS

Case / letter changes

• lower() – make lowercase

• upper() – make uppercase

• capitalize() – first char uppercase, rest lowercase

• title() – Title Case (each word)

• swapcase() – swap lower ↔ upper

• casefold() – aggressive lowercase (best for comparisons)

Trimming / removing characters

• strip([chars]) – remove leading + trailing whitespace (or given chars)

• lstrip([chars]) – remove from the left

• rstrip([chars]) – remove from the right

• removeprefix(prefix) – remove prefix if present

• removesuffix(suffix) – remove suffix if present

Searching / checking contents

• find(sub[, start[, end]]) – index or -1

• rfind(sub[, start[, end]])

• index(sub[, start[, end]]) – similar to find but raises error if not found

• rindex(sub[, start[, end]])

• count(sub[, start[, end]]) – how many times substring occurs

• startswith(prefix[, start[, end]])

• endswith(suffix[, start[, end]])

Replacing / editing

• replace(old, new[, count])

• translate(table) – replace via translation map

• maketrans(...) – helper to build translation tables (called as str.maketrans(...))

Splitting / joining

• split(sep=None, maxsplit=-1)

• rsplit(sep=None, maxsplit=-1)

• splitlines(keepends=False) – split by line breaks

• join(iterable) – join list/iterable into one string

Formatting

• format(*args, **kwargs)

• format_map(mapping)

• zfill(width) – pad with leading zeros

Alignment / padding

• center(width[, fillchar])

• ljust(width[, fillchar])

• rjust(width[, fillchar])

Character-type checks (return True/False)

• isalpha() – letters only

• isalnum() – letters or digits

• isdecimal() – decimal digits only

• isdigit() – digits (more broad than decimal)

• isnumeric() – numeric characters (broadest)

• isspace() – whitespace only

• islower() – all cased chars are lowercase

• isupper() – all cased chars are uppercase

• istitle() – title-cased

• isidentifier() – valid Python identifier?

• isprintable() – printable chars?

• isascii() – ASCII only?

Working with comparisons / sorting / partitions

• partition(sep) – split into (before, sep, after) at first sep

• rpartition(sep) – same, but last sep

• split() (already above) is often used for tokenizing

Encoding

• encode(encoding='utf-8', errors='strict')

Integer public methods

• as_integer_ratio

• bit_count

• bit_length

• conjugate

• denominator

• from_bytes

• imag

• numerator

• real

• to_bytes

Float public methods

• as_integer_ratio

• conjugate

• fromhex

• hex

• imag

• is_integer

• real