Use def keyword to define a function: def hello(): # define hello function print('Hello!') hello() # call hello function Hello!
Adding parameters to a function: def info(firstname, lastname): print(f'firstname: {firstname} | lastname: {lastname}') info('A', 'B') # call info function with argument 'A' for the parameter firstname and argument 'B' for the parameter lastname info(firstname='C', lastname='D') # explicitly naming the parameters of the function info(lastname='E', firstname='F') # the order of the arguments doesn't matter when explicitly naming the parameters firstname: A | lastname: B firstname: C | lastname: D firstname: F | lastname: E
Setting default values for the parameters: def info(firstname, lastname='unknown'): print(f'firstname: {firstname} | lastname: {lastname}') info('A') # the second argument is missing, defaults to 'unknown' info(firstname='B') # the second argument is missing, defaults to 'unknown' firstname: A | lastname: unknown firstname: B | lastname: unknown
Returning Values: def add(i, j): return i+j print(add(3, 5)) # ==> 8
Passing lists as arguments: def pop(x): return x.pop() y = [1, 2, 3] print(pop(y)) #==> 3 print(y) #==> [1, 2]
Passing a copy of a list as an argument: def pop(x): return x.pop() y = [1, 2, 3] print(pop(y[:])) #==> 3 (passing a list slice as argument) print(y) #==> [1, 2, 3]
Passing an arbitrary number of arguments: def list(*params): #==> python creates a tuple named params that will contains all the arguments print(params) list() #==> () list(1) #==> (1,) list(1, 2) #==> (1, 2) list(1, 2, 3) #==> (1, 2, 3)
Passing regular and arbitrary number of arguments: def list(key, *values): print(f'{key}={values}') #list() #==> TypeError: list() missing 1 required positional argument: 'key' list('none') #==> none=() list('one', 'a') #==> one=('a',) list('two', 'a', 'b') #==> two=('a', 'b')
Passing an arbitrary number of key-value pair as arguments: def list(**params): #==> python creates a dictionary named params that will contains all the arguments print(params) list() #==> {} list(a=1) #==> {'a': 1} list(a=1, b=2) #==> {'a': 1, 'b': 2} list(a=1, b=2, c=3) #==> {'a': 1, 'b': 2, 'c': 3}
Passing regular and arbitrary number of key-value pair as arguments: def list(key, **params): print(params[key]) #list('a') #==> KeyError: 'a' list('a', a=1) #==> 1 list('b', a=1, b=2) #==> 2 list('c', a=1, b=2, c=3) #==> 3
Storing functions in modules:
Create a file file1.py that contains the definition of two functions: #file1.py def add(i, j): return i+j def multiply(i, j): return i*j
Importing modules:
Create a file file2.py that imports the module file1 (file1.py): #file2.py import file1 # all functions defined in the module will be accessible using the prefix file1 print(file1.add(2, 3)) # calling the function add using the name of the module name as a prefix print(file1.multiply(2, 3))
Importing specific functions defined in a module:
Create a file file3.py that imports specific functions defined in the module file1 (file1.py): #file3.py from file1 import add, multiply # importing the functions add and multiply from the module file1 print(add(2, 3)) # calling directly the function add without specifying the module name print(multiply(2, 3))
Importing all functions in a module:
Create a file file4.py that imports all functions defined in the module file1 (file1.py): #file4.py from file1 import * # importing all functions from the module file1 print(add(2, 3)) # calling directly the function add without specifying the module name print(multiply(2, 3))
Using the keyword as to define an alias for a module:
Create a file file5.py that imports the module file1 (file1.py) and give it an alias f1: #file5.py import file1 as f1 # defining the alias f1 for the module file1 print(f1.add(2, 3)) # calling the function add using the alias of the module as a prefix print(f1.multiply(2, 3))
Using the keyword as to define an alias for a function:
Create a file file6.py that imports specific functions defined in the module file1 (file1.py) and give them aliases: #file6.py from file1 import add as a, multiply as m # defining the alias a for the method add and the alias m for the method multiply print(a(2, 3)) # calling directly the function add using its alias a print(m(2, 3))