Python
python [filename]
python3 [filename]
run if not modules
if __name__ == "__main__":
Loops
for idx, x in enumerate(xs):
print(idx, x)
from tqdm import tqdm
for i in tqdm(range(10000)):
...
Exceptions
Error Types:
Exception
(most general?)|RuntimeError
|TypeError
|OSError
etc
try:
x = int(input("Please enter a number: "))
break
except ValueError:
print("Oops! That was no valid number. Try again...")
except (RuntimeError, TypeError, NameError):
pass
Capture exception info
try:
raise Exception('spam', 'eggs')
break
except OSError as err:
print("OS error: {0}".format(err))
except Exception as inst:
print(type(inst))
print(inst.args)
print(inst) #Uses __str__
except:
print("Unexpected error:", sys.exc_info()[0])
raise #reraise error
Access Args
import sys
sys.argv #the list of command-line arguments with [0] being the file name
Can also use argparse
Only function scoping
if y > threshold:
x = 1
print(x)
and
and or
and
and or
0, '', [], (), {}, and None are false
Actually return one of the values being computed
'a' and 'b'
returns'b'
'' and 'b'
return''
So,
1 and a or b
is basically the trinary operator(unless a is false)(1 and [a] or [b])[0] is the safe way
Math
round(5.0000, 3) #3 is number of decimal points
'' vs ""
They are the same
== vs is
is
checks they point to the same thing i.e [1,2,3] is not [1,2,3] but [1,2,3] == [1,2,3]
Use is None
because a class could define == to be different and is is faster
Checking Packages
dir(nltk)
- lists all functions in package
Functions
KArgs & Args
*args
will give you all function parameters as a tuple
**kwargs
will give you all keyword arguments as a dictionary expect acutal args
Pass in dict like f(**dict)
to act as **kwargs
Lambdas
lambda x, y: x[1] + y
Generators
def simpleGeneratorFun():
yield 1
yield 2
yield 3
for value in simpleGeneratorFun():
print(value)
Input
PYTHON 2:
input("Enter number")
interprets user input so if int, int will be returned(Security bug, runs arbitrary code use raw_input)raw_input("Enter Your Name: ")
takes exactly what user typedPYTHON 3:
input
israw_input
Exceptions
try:
x = int(input("Please enter a number: "))
raise ValueError("Hello")
except ValueError:
print("Oops! That was no valid number. Try again...")
types
str(1) #'1'
Other
value_when_true if condition else value_when_false
Pip
#Install specific version
pip install pandas==1.3.4
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