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The Python RegEx Cheat Sheet for Budding Programmers | MakeUseOf

The Python RegEx Cheat Sheet for Budding Programmers | MakeUseOf

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The use of Python to solve various tech problems and its easy learning curve has made it one of the most popular modern programming languages. Despite being quick to learn, its regular expressions can be tricky, especially for newcomers.

Although Python has a lot of libraries, it’s wise that you know your way around its regular syntaxes. Even if you’re an expert at it, there’s a chance that you still need to occasionally look-up some Python commands to refresh your memory.

For that reason, we’ve prepared this Python regular expressions cheat sheet to help you get a better hold of your syntaxes.

FREE DOWNLOAD: This cheat sheet is available as a downloadable PDF from our distribution partner, TradePub. You will have to complete a short form to access it for the first time only. Download the Python RegEx Cheat Sheet for Budding Programmers.

The Python RegEx Cheat Sheet for Budding Programmers

Get Creative When Using Python

Learning Python’s regular expressions is a big step towards becoming a better Python programmer, but that’s just one of the few things you need to do.

However, playing around with its syntaxes and getting creative with them polishes your coding skill. So beyond learning the syntaxes, use them in real-life projects and you will become a better Python programmer.

Expression Action Examples
print() Display the result of a command x="Hello world"
print(x)

output: Hello world
input() Collect inputs from users print(input("what is your name?"))

output: what is your name?
type() Find the type of a variable x="Regular expressions"
type(x)

output:

len() Find the number of items in a variable len([1, 2, 3])

output: 3
\ Escape a character that changes the intent of a line of code print("I want you to add\"\"")

output: I want you to add""
\n Break a string character to start on the next line print("This is a line \n This is a second line")

output:
This is a line
This is a second line
def function_name(parameter):
commands		 Initiate a function with an optional parameter def yourName(x):
print(x+1)
lambda Call an anonymous function add_3_to = lambda y: y+3
print(add_3_to(4))

output: 7
return Return a result from a function def yourName(x):
return x+1
class Create a Python object class myClass:
def myFunc(x):
def __init__ Initialize the attrributes of a class class myClass:
def __init__(self, attributes…)
"__init__.py Save a file containing a module so that it’s read successfully in another Python file Rename a file containing a module as:

"__init__.py
int() Convert a variable to integer int(1.234)

output: 1
str() Convert a variable to string str(1.234)

output: ‘1.234’
float() Convert a variable to float float(23)

output: 23.0
dict(Counter()) Convert a list or a tupple into a dictionary after sorting with a Python built-in Counter from collections import Counter
dict(Counter([1,1,2,1,2,3,3,4]))

output: {1: 3, 2: 2, 3: 2, 4: 1}
round() Round up the output of an operation to the nearest whole number round(23.445)

output: 23
round(operation or number, decimal places) Round up the output of an operation to a specific number of decimal places round(23.4568, 2)

output: 23.46
if: Initiate a conditional statement if 2<3:
print("Two is smaller")
elif: Make a counterstatement when the if statement is False if 2<3:
print("Two is smaller")
elif 2==3:
print("Go on")
else: Make a final counterstatement if other conditions are False if 2<3:
print("Two is smaller")
elif 2==3:
print("Go on")
else:
print("Three is greater")
continue Ignore a condition and execute the rest of the loop a=[1, 4, -10, 6, 8]
for b in a:
if b<=0:
continue
print(b)

output:
1
4
6
8
break Terminate the flow of a loop with a given condition a=[1, 4, -10, 6, 8]
for b in a:
if b>=6:
break
print(b)

output:
1
4
-10
pass Ignore a set of prior instructions for b in a:
pass
try, except Try a block of code, else, raise a defined exception try:
print(a)

except:
print("An error occured!")

output: An error occured!
finally Execute a final code when the try and the except blocks fail try:
print(a)

except:
print(d)
finally:
print("You can’t print an undefined variable")

output: You can’t print an undefined variable
raise Exception() Raise an exception that stops the command when execution isn’t possible a=7+2
if a<10:
raise Exception("Oh! You didn’t get a score of 10")
import x Import a whole module or library import math
from x import y Import a library x from a file, or a class y from scipy.stats import mode
as Customize an expression to your preferred name import pandas as pd
in Check if a value is present in a variable x=[1, 4, 6, 7]
if 5 in x:
print("There is a five")
else:
print("There is no five")

output: There is no five
is Check if two variables refer to a single element x=[1, 4, 6, 7]
x=b
print(x is b)
True
None Declare a null value x=None
< Check if one value is lesser than another 5<10

output: True
> Check if one value is more than another 5>10

output: False
<= Check if a value is lesser or equal to another 2*2<=3

output: False
>= Check if a value is greater or equal to another 2*2>=3

output: True
"== Check if a value is exactly equal to the other 3==4

ouput: False
!= Ascertain that a value is not equal to the other 3!=4

ouput: True
import re Import Python’s built-in regular expressions import re
re.findall("strings", variable)
a|b Check if either of two elements are present in a string import re
someText="Hello regular expression"
a=re.findall("regular|Hello", someText)
print(a)

output: [‘Hello’, ‘regular’]
string$ Check if a variable ends with a set of strings import re
someText="Hello regular expression"
a=re.findall("expression$", someText)

output: [‘expression’]
^string Check if a variable starts with a set of strings import re
someText="Hello regular expression"
a=re.findall("^Hello", someText)
print(a)

output: [‘Hello’]
string.index() Check the index position of a string character a= "Hello World"
a.index(‘H’)

output: 0
string.capitalize() Capitalize the first character in a set of strings a= "Hello World"
a.capitalize()

output: ‘Hello world’

string.swapcase() Print the first letter of each word as a lower case and the others as upper case a= "Hello World"
a.swapcase()

output:
‘hELLO wORLD’
string.lower() Convert all the strings to a lowercase a= "Hello World"
a.lower()

output: ‘hello world’
string.upper() Convert all strings to uppercase a= "Hello World"
a.upper()

output: ‘HELLO WORLD’
string.startswith() Check if a string starts with a particular character a= "Hello World"
a.startswith(‘a’)

output: False
string.endswith() Check if a string ends with a particular character a= "Hello World"
a.endswith(‘d’)

output: True
string.split() Separate each word into a list a= "Hello World"
a.split()

output: [‘Hello’, ‘world’]
strings {}’.format() Display an output as string a=3+4
print("The answer is {}".format(a))

output: The answer is 7
is not None Check if the value of a variable is not empty def checknull(a):
if a is not None:
return "its full!"
else:
return "its empty!"
x%y Find the remainder (modulus) of a division 9%4

output: 1
x//y Find the quotient of a division 9//4

output: 2
"= Assign a value to a variable a={1:5, 3:4}
"+ Add elements together ["a two"] + ["a one"]

output: [‘a two’, ‘a one’]

1+3

output=4
"- Find the difference between a set of numbers 3-4

output=-1
"* Find the product of a set of numbers 3*4

output:12
a+=x Add x to variable a without assigning its value to a new variable a=2
a+=3

output: 5
a-=x Subsract x from variable a without assigning it to a new variable a=3
a-=2

output: 1
a*=x Find the product of variable a and x without assigning the resullt to a new variable a=[1, 3, 4]
a*=2

output: [1, 3, 4, 1, 3, 4]
x**y Raise base x to power y 2**3

output: 8
pow(x, y) Raise x to the power of y pow(2, 3)

output: 8
abs(x) Convert a negative integer to its absolute value abs(-5)

output: 5
x**(1/nth) Find the nth root of a number 8**(1/3)

output: 2
a=b=c=d=x Assign the same value to multiple variables a=b=c=d="Hello world"
x, y = y, x Swap variables x = [1, 2]
y = 3
x, y = y, x
print(x, y)

output:
3 [1, 2]
for Loop through the elements in a variable a=[1, 3, 5]
for b in a:
print(b, "x", "2", "=", b*2)

output:
1 x 2 = 2
3 x 2 = 6
5 x 2 = 10
while Keep looping through a variable, as far as a particular condition remains True a=4
b=2
while b<=a:
print(b, "is lesser than", a)
b+=1

output:
2 is lesser than 4
3 is lesser than 4
4 is lesser than 4
range() Create a range of positive integers between x and y x=range(4)
print(x)
range(0, 4)
for b in x:
print(b)

output:
0
1
2
3
sum() Iterate through the elements in a list print(sum([1, 2, 3]))

output:6
sum(list, start) Return the sum of a list with an added element print(sum([1, 2, 3], 3))

output: 9
[] Make a list of elements x=[‘a’, 3, 5, ‘h’, [1, 3, 3], {‘d’:3}]
() Create a tupple—tupples are immutable x=(1, 2, ‘g’, 5)
{} Create a dictionary a={‘x’:6, ‘y’:8}
x[a:b] Slice through a list x=[1, 3, 5, 6]
x[0:2]

output: [1, 3]
x[key] Get the value of a key in dictionary x a={‘x’:6, ‘y’:8}
print(a[‘x’])

output: 6
x.append() Add a list of values to an empty list x=[1]
x.append([1,2,3])
print(x)

output: [1, [1,2,3]]
x.extend() Add a list of values to continue an existing list without necessarily creating a nested list x=[1,2]
x.extend([3,4,6,2])
print(x)

output:
[1, 2, 3, 4, 6, 2]
del(x[a:b]) Delete an item completely from a list at a specific index x=[1,2,3,5]
del(x[0:2])
print(x)

output: [2,3,5]
del(x[key]) Delete a key and a value completely from a dictionary at a specific index y={1:3, 2:5, 4:6, 8:2}
del(y[1], y[8])
print(y)

output= {2:5, 4:6}
dict.pop() Pop out the value of a key and remove it from a dictionary at a specific index a={1:3, 2:4, 5:6}
a.pop(1)

output: 3
dict.popitem() Pop out the last item from a dictionary and delete it a={1:2, 4:8, 3:5}
a.popitem()

output: (3, 5)
print(a)
output: {1:2, 4:8}
list.pop() Pop out a given index from a list and remove it from a list a=[1, 3, 2, 4, 1, 6, 6, 4]
a.pop(-2)

output: 6
print(a)
output: [1, 3, 2, 4, 1, 6, 4]
clear() Empty the elements of a list or a dictionary x=[1, 3, 5]
x.clear()
print(x)

output: []
remove() Remove an item from a list x=[1, 5, 6, 7]
x.remove(1)

output: [5, 6, 7]
insert() Insert elements into a llist x=[3, 5, 6]
x.insert(1, 4)
print(x)

output: [1, 4, 3, 5, 6]
sort(reverse=condition) Reverse the direction of the elements in a list x=[1, 3, 5, 6]
x.sort(reverse=True)
print(x)

output: [6, 5, 3, 1]
update() Update a dictionary by changing its first element and adding any other item to its end x={1:3, 5:6}
x.update({1:4, 8:7, 4:4})
print(x)

output: {1: 4, 5: 6, 8: 7, 4: 4}
keys() Show all the keys in a dictionary a={1:2, 4:8}
a.keys()

output: dict_keys([1, 4])
values() Show all the values in a dictionary a={1:2, 4:8}
a.values()

output: dict_values([2, 8])
items() Display the keys and the values in a dictionary a={1:2, 4:8}
a.items()

output: dict_items([(1, 2), (4, 8)])
get(key) Get the value of an item in a dictionary by its key a={1:2, 4:8, 3:5}
a.get(1)

output: 2
setdefault(key) Return the original value of an element to a dictionary a.setdefault(2)
f={**a, **b} Merge two dictionaries a={‘x’:6, ‘y’:8}
b={‘c’:5, ‘d’:3}
f={**a, **y}
print(f)

output:{‘x’: 6, ‘y’: 8, ‘c’: 5, ‘d’: 3}
remove() Remove the first matching value of an element from a list without minding its index a=[1, 3, 2, 4, 4, 1, 6, 6, 4]
a.remove(4)
print(a)

output: [1, 3, 2, 4, 1, 6, 6, 4]
memoryview(x) Access the internal buffers of an object a=memoryview(object)
bytes() Convert a memory buffer protocol into bytes bytes(a[0:2])
bytearray() Return an array of bytes bytearray(object)
# Write a single line of comment or prevent a line of code from being executed # Python regex cheat sheet
""" """ Write a multi-line comment """The Python regex cheat sheet is good for beginners
It’s equally a great refresher for experts"""
Command Line
pip install package Install an online library pip install pandas
virtualenv name Use virtaulenv to create a virtual environment virtualenv myproject
mkvirtualenv name Use virtual environment wrapper to create virtual environment mkvirtualenv myproject
python file.py Run the commands in a Python file "python my_file.py
pip freeze List out all the installed packages in a virtual environment pip freeze
pip freeze > somefiles Copy all installed libraries in a single file pip freeze > requirements.txt
where Find the installation path of Python where python
–version Check the version of a package python –version
.exe Run a Python shell python.exe
with open(file, ‘w’) Write to an existing file and overwrite its existing content with open(‘regex.txt’, ‘w’) as wf:
wf.write("Hello World!")
with open(file, ‘r’) Open a file as read-only with open(‘regex.txt’, ‘r’) as rf:
print(rf.read()
with open(file, ‘a’) Write to a file without overwriting its existing content with open(‘regex.txt’, ‘a’) as af:
af.write("\nHello Yes!")
file.close Close a file if it’s not in use af=open(‘regex.txt’)
af.close
exit Exit the Python shell exit()

non critical

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November 7, 2020 at 03:10PM