Python Review · Conditions, Loops, Context Managers
Jan 16, 2016
|
Tech
Software
Conditional Statements
-
if-elif-else
:
logical branching.
Truthy Falsy Values
if obj:
,
while executing it, Python evaluates the following internal logic:
-
bool(): Python first calls for this method; if it exists, its return value
(True/False) is used;
-
len(): otherwise, Python calls len(obj); if the
result is 0, it returns True; otherwise, it returns False;
-
if neither method is defined, the object is always considered
True;
-
note that values such as
None, 0, 0j, ""
evaluate to False.
Conditional Expressions
| Scenario |
Code Example |
| Basic Assignment |
x = a if cond else (b if cond2 else c) |
| Container Comprehension |
lst = [a if cond else b for x in list] |
| Lambda Functions |
func = lambda x: a if cond else b |
| Short-Circuit Logic |
var = name or "Default Value" |
Looping
-
for, for-break-else
:
iterates over a sequence.
-
while, do-while
:
repeats a code block while a certain condition remains True.
Loop Control
-
break
:
terminates a loop, inner loop if nested, and executes the line after the loop.
-
continue
:
skips remaining code in a loop, inner loop if nested, and starts the next
iteration.
-
pass
:
a syntactical placeholder that does nothing.
Context Manager
-
with
:
automatically handles exceptions, resource allocation and deallocation.