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names = ("John", "Lisa", "Terminator", "Python")
Don't do this.
semicolon_separated = names[0]
for name in names[1:]:
semicolon_separated += ";" + name
print(semicolon_separated)
John;Lisa;Terminator;Python
join instead!¶semicolon_separated = ";".join(names)
print(semicolon_separated)
John;Lisa;Terminator;Python
or in assignments¶The return value of a or b:
a if a is truthyb otherwiseYou can take advantage of this e.g. while writing variable assignments.
a = 0
b = None
c = "John Doe"
Instead of doing something like this:
my_variable = "default value"
if a:
my_variable = a
elif b:
my_variable = b
elif c:
my_variable = c
print(my_variable)
John Doe
my_variable = a or b or c or "default value"
print(my_variable)
John Doe
try - except - else¶Don't use the following technique for checking if there was exceptions during execution of some block of code.
exception_occured = False
try:
# here would be the logic of your master piece
bad_calculation = 1 / 0
except ValueError as e:
print(f"Oh boi, some value error: {e}")
exception_occured = True
except Exception as e:
print(f"Oh boi, something bad happened: {e}")
exception_occured = True
if not exception_occured:
print("All went well!")
Oh boi, something bad happened: division by zero
try:
# here would be the logic of your master piece
bad_calculation = 1 / 0
except ValueError as e:
print(f"Oh boi, some keyerror: {e}")
except Exception as e:
print(f"Oh boi, something bad happened: {e}")
else:
print("All went well!")
Oh boi, something bad happened: division by zero
try - finally¶For scenarios where you want to do something always, even when there are exceptions.
Don't do it like this
def magical_calculation():
try:
# here would be the logic of your master piece
result = 1 / 0
except ZeroDivisionError:
print("This could be something important that should be done every time")
return 0
except Exception:
print("This could be something important that should be done every time")
return None
print("This could be something important that should be done every time")
return result
print(f"return value: {magical_calculation()}")
This could be something important that should be done every time return value: 0
def magical_calculation():
try:
# here would be the logic of your master piece
result = 1 / 0
except ZeroDivisionError:
return 0
except Exception:
return None
finally:
print("This could be something important that should be done every time")
return result
print(f"return value: {magical_calculation()}")
This could be something important that should be done every time return value: 0
Note: You can also have try-except-else-finally structure. In cases where exception is not raised inside try, else will be executed before finally. If there is an expection, else block is not executed.
One use case example is file I/O.
Don't play with files like this.
try:
some_file = open("tmp.txt", "w")
print(f"the file is now open: {not some_file.closed}")
# here would be some logic
finally:
some_file.close()
print(f"now it's closed: {some_file.closed}")
the file is now open: True now it's closed: True
with open("tmp.txt", "w") as some_file:
print(f"the file is now open: {not some_file.closed}")
# here would be some logic
print(f"now it's closed: {some_file.closed}")
the file is now open: True now it's closed: True
from contextlib import contextmanager
@contextmanager
def my_context():
print("Entering to my context")
yield
print("Exiting my context")
def do_stuff():
with my_context():
print("Doing stuff")
print("Doing some stuff outside my context")
do_stuff()
Entering to my context Doing stuff Exiting my context Doing some stuff outside my context
min() & max()¶secret_data = (1, 2, 5, 99, 8, -9)
No need to bake it yourself.
max_value = 0
for val in secret_data:
if val > max_value:
max_value = val
print(max_value)
99
max_value = max(secret_data)
print(max_value)
99
contextlib.suppress - ignoring exceptions¶If there's a potential exception that is ok, don't handle it like this.
value = 0
try:
value = 1 / 0 # just for demonstrating purposes
except ZeroDivisionError:
pass
print(value)
0
from contextlib import suppress
value = 0
with suppress(ZeroDivisionError):
value = 1 / 0 # just for demonstrating purposes
print(value)
0
Instead of doing something like this.
class Person:
def __init__(self, first_name, last_name):
self.first_name = first_name
self.last_name = last_name
def get_full_name(self):
return f"{self.first_name} {self.last_name}"
def set_full_name(self, full_name):
parts = full_name.split()
if len(parts) != 2:
raise ValueError("Sorry, too difficult name")
self.first_name, self.last_name = parts
p = Person("John", "Doe")
print(p.get_full_name())
p.set_full_name("Lisa Doe")
print(p.get_full_name())
John Doe Lisa Doe
class Person:
def __init__(self, first_name, last_name):
self.first_name = first_name
self.last_name = last_name
@property
def full_name(self):
return f"{self.first_name} {self.last_name}"
@full_name.setter
def full_name(self, name):
parts = name.split()
if len(parts) != 2:
raise ValueError("Sorry, too difficult name")
self.first_name, self.last_name = parts
p = Person("John", "Doe")
print(p.full_name)
p.full_name = "Lisa Doe"
print(p.full_name)
John Doe Lisa Doe