Functions

Scopes

Local	Global	Built-ins	Non-local
No specific arguyment needed	preceeding argument global variable_name needed to initialize the variable value from a global parameter	such as sum(), tuple(), abs()	Requires a keyword nonlocal to emphasize that the variable is not local in a nested function.

Function with multiple and variable inputs using def keyword

def func1():
	x=1
	print(x)
 
func1() # prints 1
 
def func2(x,n=1): # creates a variable n with default parameter 1
	sq = x**n
	return sq
print(func2(4,3)) # Prints 64
 
def func3(*args): # Function with variable non-keyworded input parameters
	sum_all=0
 
	for i in args:
		sum_all = sum_all + i
 
	print(sum_all)
 
func3(2,3,4)
 
def func4(**kwargs): # Function with variable kew-worded input parameters, by default it creates a dictionary of all niput parameters to be looped over later
	
	print("\n New Person")
	for key, value in kwargs.items():
		print(key + ':' + value)
 
	print("\n Entry Completed")
 
func4(Name='Daniel',Occupation='Carpenter',Salary='100000')
 
## This will print:
#  New Person
# Name:Daniel
# Occupation:Carpenter
# Salary:100000
#
# Entry Completed

lambda functions - For oneline functions

Example:

func_lambda = lambda x,y:x**y
output = func_lambda(2,3)
print(output)

Prints 8, which is 2 raised to 3.

Error messages and exceptions

• Can be done using try, except and raise inside the function

For Example:

def errors_func_sqrt(x):
	# if x<0:
	#	raise ValueError('x must be non-negative')
	try: # will try to execute this
		sq = x** -0.5
	except TypeErrror: # Excluding only TypeErrors
		print('x must be int or float')

Now, if we pass errors_func_sqrt(-9) when the if statement line is uncommented, it will raise the ValueError, is we pass errors_func_sqrt('hi'), it will raise the TypeError and print the statement which we asked for.

Using docstrings

• docstrings are function information written between ''' and ''' using standard formats
• Google style or Numpy docstring standard can be accessed using function.__doc__ or using the package inspect which can be called by inspect.getdoc(function)

Using context manager

• A compound statement such as with is used to open a context_manager

with open("file.txt") as myf:
	text = myf.read() 
 
n = 0
for word in text.split():
	if word.lower() == ['bubblegum']
		n = 0
 
print(n) # Prints out number of times bubblegum word appears in the read file.

• Writing context manager using either classes or a function using the keyword yield and using the @contextlib.contextmanager decorator (which is a text that goes before the context manager function definition)

@contextlib.contextmanager
def open_read_only(filename):
  """Open a file in read-only mode.
 
  Args:
    filename (str): The location of the file to read
 
  Yields:
    file object
  """
  read_only_file = open(filename, mode='r')
  # Yield read_only_file so it can be assigned to my_file
  yield read_only_file
  # Close read_only_file
  read_only_file.close()
 
with open_read_only('my_file.txt') as my_file:
  print(my_file.read())

The above code will open a file as a read_only, as specified within the content manager function

• In order to make sure some part of the code runs (such as closing a file) regardless of some error in coding, use try, except, and finally statements:

try:
    # code that may cause exceptions
except:
    # code that handle exceptions
finally:
    # code that runs regardless of the other two statements