Introduction
I occasionally write scripts in Python 3 and this article keeps track of basic syntax that is frequently used according to my experience. To keep things simple, this article is focus on language syntax and does not include framework or tooling of the Python ecosystem. Code written here is tested and hosted on GitHub. I hope that it will be useful for you as well. Enjoy!
Data Container
This section discusses about list, set, and dictionary.
Container Creation
Create a dictionary, list, set:
import typing
# dictionary
my_dict1 = {"k1": "v1", "k2": "v2", "k3": "v3"}
my_dict2 = dict()
my_dict3 = typing.OrderedDict()
# list
my_list1 = ["v1", "v2", "v3"]
my_list2 = list()
my_list3 = [0] * 4 # [0, 0, 0, 0]
# set
my_set1 = {"k1", "k2", "k3"}
my_set2 = set()
Container Iteration
Iterate keys of a dictionary:
for key in my_dict:
print(key)
Iterate values of a dictionary:
for value in my_dict.values():
print(value)
Iterate key-value pairs of a dictionary:
for key, value in my_dict.items():
print(key, value)
Iterate item in a list:
for item in my_list:
print(item)
Iterate index and item in a list:
for i, item in enumerate(my_list):
print(i, item)
List Comprehension
List comprehensions are used for creating new lists from other iterables like tuples, strings, arrays, lists, etc. A list comprehension consists of brackets containing the expression, which is executed for each element along with the for loop to iterate over each element.
new_list = [ expression(element) for element in old_list if condition ]
Examples:
>>> my_dict = {'k1': 'v1', 'k2': 'v2'}
>>> [v for v in my_dict.values()]
['v1', 'v2']
>>> [k for k in my_dict]
['k1', 'k2']
>>> [k for k in my_dict if k == 'k1']
['k1']
>>> [k + ':' + v for k, v in my_dict.items()]
['k1:v1', 'k2:v2']
Container Insertion
Append an element into list or replace an existing element:
my_list.append(e)
my_list[1] = e
Add an element into set:
my_set.add(e)
Add a new entry into dictionary or increment an existing value:
my_dict["my_key"] = 2
my_dict["my_key] += 1
Container Functions
| Function | Sample | Description |
|---|---|---|
len |
len(my_list) |
The length of the container. |
enumerate |
enumerate(my_list) |
Add counter to the iterable. |
max |
max(my_list) |
The maximal value among the given items. |
min |
min(my_list) |
The minimal value among the given items. |
reversed |
reversed(my_list) |
Create a reverse-iterator for a given list. |
If Statement
Ternary operator:
TrueExpression if Condition else FalseExpression
>>> l = []
>>> 'not empty' if l else 'empty'
'empty'
Math
| Function | Sample | Description |
|---|---|---|
Floor division, integer division (//) |
7 // 2 |
3 |
Float division (/) |
7 / 2 |
3.5 |
Class
class Dog:
kind = 'canine' # class variable shared by all instances
def __init__(self, name):
self.name = name # instance variable unique to each instance
String Manipulations
Hint: hit TAB in Python REPL to see auto-completion for the string functions.
| Category | Function | Description |
|---|---|---|
| Whitespace | strip() |
Trim the string |
| Whitespace | lstrip() |
Left trim |
| Whitespace | rstrip() |
Right trim |
| Case | lower() |
Lower case |
| Case | upper() |
Uppder case |
| Split | split(), split(sep) |
Split the string using whitespace or a seperator |
| Cancatenation | join(words) |
Join words together using a given string |
Splitting string with different methods:
import re
# regex without max-split
re.split(pattern, text)
# regex with max-split
re.split(pattern, text, maxsplit=2)
# split with normal separator (no regex)
text.split(sep)
References
- GeeksforGeeks, “Python – List Comprehension”, GeeksforGeeks, 2021.
- Python, “collections - Container datatypes - Python 3.10.0”, Python Documentation, 2021.
- Python, “Classes”, Python Documentation, 2021.