| title | description | created | updated |
|---|---|---|---|
Python |
Python cheatsheet contains useful code syntax with examples which is handy while coding. |
2020-04-24 |
2020-04-24 |
print("hello world")#is used to comment a line in Python
| Category | Data Type |
|---|---|
| Text | str |
| Number | int, float, complex |
| Boolean | bool |
| Binary | bytes, bytearray, memoryview |
| Set | set, frozenset |
| Sequence | list, tuple, range |
| Mapping | dict |
| None | NoneType |
- type() is used to know the data type of a variable
| Constructor function | desc |
|---|---|
| int() | constructs an integer from any form of data like string, float or integer |
| float() | constructs a float number from any form of data like string, float or integer |
| str() | constructs a string from any form of data like string, float or integer |
In Python, Type casting or type converion is the method to convert one data-type to another data-type. Basically there are 2 types of type casting:
1:Implicit This method of type casting is performed by the machine or the python interpreter itself. There is no need to define externally.
2:Explicit In this method of type casting,the user performs the changes by using the predefined functions externally.There can be a loss of data in this type of type conversion
In Python, declaring variables is not required. Means you don't need to specify whether it is an integer or string etc as Python is a dynamically typed language.
| Type | Operators |
|---|---|
| Arithmetic Operators | + - * / % ** // |
| Comparision Operators | == != > >= < <= |
| Bitwise Operators | & ^ | ^ ~ << >> |
| Logical Operators | && || ! |
| Assignment Operators | = += -= *= /= %= **= //= |
| Membership Operators | in, not in |
| Identity Operators | is, is not |
# declaring a function
def function-name(parameters){ # here parameters are optional
#code
}
function-name(parameters); # calling a functionList is ordered collection of items and can be changed. [] are used to represent lists.
mylist=["iPhone","Pixel","Samsung"]
print(mylist[0]) # prints iPhone
print(mylist[7]) # throws IndexError : list index out of range
print(mylist[-1]) # prints Samsung| Operation | Description |
|---|---|
| lst.append(val) | add an item to list at end |
| lst.extend(seq) | add sequence of items to list at end |
| lst.insert(index,val) | insert an item at given index |
| lst.remove(val) | remove first item with value val |
lst.pop([index])→value |
remove & return item at index |
| lst.sort() | sort the given list items |
| lst.reverse() | reverse the given list items |
| lst.count() | Returns the number of elements with the specified value |
| lst.clear() | Removes all the elements from the list |
| lst.index() | Returns the index of the first element with the specified value |
| lst.copy() | Returns a copy of the list |
Tuple is ordered collection of items and can't be changed. () are used to represent Tuples.
myTuple = ["iPhone","Pixel","Samsung"]
print(myTuple[0]) # prints iPhone
print(myTuple[7]) # throws IndexError: tuple index out of range
print(myTuple[-1]) # prints SamsungSet is unordered collection of items and it is unindexed. {} are used to represent sets.
mySet = {"iPhone", "Pixel", "Samsung"}
mySet.add('OnePlus')
print(mySet) # prints {'iPhone', 'Samsung', 'OnePlus', 'Pixel'}| Method | Description | Usage |
|---|---|---|
| add() | to add an element to the set | mySet.add('value') |
| clear() | to remove all the elements from the set | mySet.clear() |
| pop() | to remove last element from the set | mySet.pop() |
| remove() | to remove a specified element from the set | mySet.remove("value") |
| del() | to delete a set | del myset |
| copy() | to return a copy of the set | copySet = mySet.copy() |
| union() | to return a set containing the union of sets | mySet3 = mySet1.union(mySet2) |
| update() | to update the set with the union of this set and others | mySet1.update(mySet2) |
Dictionary is a collection of key value pairs which is unordered, can be changed, and indexed. They are written in curly brackets with key - value pairs.
mydict = {
"brand" :"iPhone",
"model": "iPhone 11"
}
val = mydict["brand"]
print(val) # prints iPhone| Operation | Description |
|---|---|
d[key]=value |
To add a new key-value pair to dictionary or to change it's value if key is existing |
| d.copy() | Returns a copy of the dictionary |
| d.keys() | Returns a list containing all the dictionary's keys |
| d.values() | Returns a list of all the values in the dictionary |
| d.items() | Removes the element with the specified key |
| d.clear() | To empty the dictionary items. |
del d[key] |
To remove an item from a dictionary. |
| d.pop(key) | To remove an item from a dictionary. |
| d.popitem() | removes the item that was last inserted into the dictionary |
| d.get(key) | Returns the value of the specified key |
| d.setdefault(key) | Returns the value of the specified key. If the key does not exist then returns the default value provided |
| d.fromkeys(key,value) | Returns a dictionary with specified keys and values |
if conditional-expression :
#codeif conditional-expression :
#code
else :
#codeif conditional-expression :
#code
elif conditional-expression :
#code
else :
#codeThe try block lets you test a block of code for errors. The except block lets you handle the error.
try:
print(1/0)
except:
print("You can't divide by zero!")The finally block lets you execute code, regardless of the result of the try- and except blocks.
try:
print(x)
except:
print("Variable x is not defined")
finally:
print("The program is finished.")You can define as many exception blocks as you want, e.g. if you want to execute a special block of code for a special kind of error.
a = input("Digit a number: ")
try:
b = [i for i in range(int(a))]
print(b[3])
except ValueError:
print("You didn't digit a number.")
except IndexError:
print("Your list have less than 4 numbers.")
finally:
print("Python is cool.")For loop is used to iterate over arrays(list, tuple, set, dictionary) or strings.
for variable in arrays :
#codewhile condition
#code | str.strip() | str.lower() | str.upper() |
| str.replace("str to be replaced","new string to replace") | str.split("seperator") | len(str) |
| + for concatenation | str.count(substr) | str.find(substr) |
| str.index(substr, start, end) | str.join(array) | str.partition(substr) |
| str.zfill(len) | str.swapcase() | str.isdecimal() |
| str.isdigit() | str.islower() | str.isupper() |
| str.endswith(value, start, end) | str.startswith(value, start, end) | str.isspace() |
Install a python driver pymongo to connect with MongoDB.
import pymongo
db = pymongo.MongoClient("mongodb://localhost:27017/")
mydb = db["sample"]import pymongo
db = pymongo.MongoClient("mongodb://localhost:27017/")
mydb = db["sample"]
mycln = mydb["details"]#insert a single document
doc = mycln.insert_one(mydict)
# insert multiple documents
mylist =[
{"name": "foo", "age": 20},
{"name": "bar", "age": 25},
{"name": "apple", "age": 30}
]
doc1 = mycln.insert_many(mylist)#to return all the documents
for doc in mycln.find():
print(doc)
# to return first occurence
doc1=mycln.find_one()
print(doc1)# to update a single document
mycln.update_one({"name" : "foo"}, {"$set":{"age": 23}})# to delete a single document
doc1 = mycln.delete_one({"name" : "foo"})Use open() function with c or a or w as mode.
file = open("myfile.txt","c")Use open() function with r as mode.
file = open("myfile.txt","r")
print(file.read())Use open() function with a or w as mode.
file = open("myfile.txt","a")
file.write("Happy learning!!")
file.close()For deleting files, you must import os module and use os.remove() function.
import os
os.remove(filename)