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Python Basics Cheat Sheet (DRAFT) by

Beginners guide for Python

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Comments in python

#
For a single line comment.
 
 '''
For a multiple line comment
 
 "­"­" 

"""

For a multiple line comment

Useful commands

"­\n"
Jumps to a different line.
 
"­\t"
Gives some spaces.
 
#%%
Creates a chunk of code.

Python Variab­les

string
Holds text based values
 
int
Interger numbers
 
float
Decimal numbers
 
boolean
True or False
There are also list, tuples and dictio­naries.

To see what are the types of the variables we are working with: 
type(_)

Guidel­ines:

- Use descri­ptive names.
- Be consis­tent.
- Keep length in check.

You can't use spaces not dots (.) when defining names

Values

input(­"­__")
Returns a string
 
type( )
Checks the type
 
isinst­ance(x, float)
Checks what you ask
Converting values
 
float(x)
Converts x to float
 
int(x)
Converts x to interger
 
str(x)
Converts x to string
 
bool(x)
Converts x to boolean
Creating values
 
range (start, stop[, step])
You can create a range or usea a given

Math­ema­tical operat­ions

+
Addition
 
 -
Substr­action
 
*
Multip­lic­ation
 
/
Division
 
%
Modulus
 
**
Exponent
 
//
Floor division
There also exist a library called 
math
to make other kind of mathem­atical operations

We can use this with numbers and booleans
  

String methods

len(s)
Calculate the lenght
 
+
Add two strings
 
*
Repeat a string
 
s.find(x)
Finds the first position of x in the string
 
s.count(x)
Counts the number of times x is in the string
 
s.upper()
All in upper case
 
s.lower()
All in lower case
 
s.title()
First letter upper case
 
s.repl­ace­(x,y)
Replace x by y
 
s.strip()
Strips spaces at the end
 
s.split()
Splits in whatever you say

Cond­iti­ons

"­__" in [ ]
Is something in.
 
"­__" not in [ ]
Is something not in.
 
>
Larger than
 
<
Lower than
 
>=
Larger or equal than
 
< =
Lower or equal than
 
==
Equal to something
 
!=
Not equal to something
 
and
 
or
 
not

Functions

def functi­on_name ( arg1,arg2):
 command1
command2
command3
return variable
You just have to use the name of the function with the number of variables that you have arrange.
 
def functi­on_name ( *args):
 command1
command2
command3
return variable
When you don't know the number of arguments that you want to use, you just use the * with the args.
 
def functi­on_name ( **kwargs):
 command1
command2
command3
return variable
With dictio­naries
Lambda functions
It returns the value with a single expres­sion, the can not obtain commands or more than one expression
 
g=lambda x:x+2
Map functions
 
map()
Takes a function and an iterable like a list as arguments and applies the function to each item in the iterable.
When using functions you can use the command you want for the result, but is better using return instead of print because you can assign the result to a variable
  

Bool­eans

Displayed as:
 
True
 
False
Different than R

Cond­iti­onals

if __a __ :
       do this
elif __:
       do this
else:
       do this
The form of arrange is important, while you are under a condition you have to write inside it

While Loops:

while condition:
     statement1
     statement2
     statement3
In this kind of loops, while the condition is still true, it continues happening.

Helping in While Loops:

continue
Skips the current iteration and go to the next one
 
break
Halts the execution of a loop entirely
Both of them are useful to avoid infinite loops

For Loops

for i in list/range:
     statement1
     statement2
     statement3
A for loop is a control flow statement for specifying iteration, which allows code to be executed repeat­edly.

Library random

randint(a, b)
creates values from the range you ask
For using the library you have to import it:

import random


Then, for using it, you need to say that you are going to look for the function in the library. If you want to avoid it you can import just one function from the library.

Helping in For Loops:

continue
Skips the current iteration and go to the next one
 
break
Halts the execution of the loop entirely
These commands continue and break are useful to avoid infinite loops