Let’s talk about what are the most commonly used statements and functions in Python?

1. Built-in functions

Built-in functions are the function methods that come with Python, you can use them as you like, such as zip, filter, isinstance, etc.

The following is a list of built-in functions given by Python official documents, which is quite complete

The following are common built-in functions:

1. enumerate(iterable,start=0)

enumerate() is a built-in function of python, which means enumeration and enumeration.

For an iterable/traversable object (such as a list, string), enumerate forms an index sequence, which can be used to obtain the index and value at the same time.

The usage of enumerate in python is mostly used to get the count in the for loop.

seasons = ['Spring', 'Summer', 'Fall', 'Winter']
list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

2. zip(*iterables,strict=False)

zip() function is used to take an iterable object as a parameter and pack the corresponding elements in the object into tuples. , and then returns a list of these tuples.

If the number of elements in each iterator is inconsistent, the length of the returned list is the same as the shortest object. Using the * operator, the tuple can be decompressed into a list.

zip(iterable1,iterable2, ...).

>>> for item in zip([1, 2, 3], ['sugar', 'spice', 'everything nice']):
... print(item)
...
(1, 'sugar')
(2, 'spice')
(3, 'everything nice')

3. filter(function,iterable)

Filter filters a sequence, returns an iterator object, and removes sequences that do not meet the conditions.

filter(function,data).

function serves as a conditional selection function.

For example, define a function to check whether the input number is an even number. It will return True if the number is even, otherwise it will return False.

def is_even(x):
if x % 2 == 0:
return True
else:
return False

Then use filter to filter a list:

l1 = [1, 2, 3, 4, 5]
fl = filter(is_even, l1)
list(fl)

4. isinstance(object,classinfo)

isinstance is used to determine whether a variable or object is It is not a function of a certain type.

If the parameter object is an instance of classinfo, or object is an instance of a subclass of the classinfo class, return True. If object is not an object of the given type, the return result is always False.

>>>a = 2
>>> isinstance (a,int)
True
>>> isinstance (a,str)
False
>>> isinstance (a,(str,int,list))# 是元组中的一个返回 True
True

5. eval(expression[,globals[,locals]])

eval is used to evaluate the string str as a valid expression and return the calculation result.

Expression parses the parameter expression and evaluates it as a Python expression (technically a list of conditions), using the globals and locals dictionaries as global and local namespaces.

>>>x = 7
>>> eval( '3 * x' )
21
>>> eval('pow(2,2)')
4
>>> eval('2 + 2')
4
>>> n=81
>>> eval("n + 4")
85

Commonly used sentence patterns

In the daily coding process, there are actually many commonly used sentence patterns, which appear very frequently and are also common writing methods.

1. format string formatting

format treats the string as a template and formats it through the passed parameters. It is very practical and powerful.

# 格式化字符串
print('{} {}'.format('hello','world')) 
# 浮点数
float1 = 563.78453
print("{:5.2f}".format(float1))

2. Connect strings

Use to connect two strings.

string1 = "Linux"
string2 = "Hint"
joined_string = string1 + string2
print(joined_string)

3. if...else conditional statement

Python conditional statement is a code block that is executed based on the execution result (True or False) of one or more statements.

The if...else statement is used to execute situations that require judgment.

# Assign a numeric value
number = 70

# Check the is more than 70 or not
if (number >= 70):
print("You have passed")
else:
print("You have not passed")

4. for...in, while loop statements

The loop statement is to traverse a sequence and perform a certain operation in a loop. The loop statements in Python include for and while.

for loop:

# Initialize the list
weekdays = ["Sunday", "Monday", "Tuesday","Wednesday", "Thursday","Friday", "Saturday"]
print("Seven Weekdays are:n")
# Iterate the list using for loop
for day in range(len(weekdays)):
print(weekdays[day])

while loop:

# Initialize counter
counter = 1
# Iterate the loop 5 times
while counter < 6:
# Print the counter value
print ("The current counter value: %d" % counter)
# Increment the counter
counter = counter + 1

5. Import function to import other scripts

Sometimes you need to use a script in another python file , this is actually very simple, just like using the import keyword to import any module.

vacations.py:

# Initialize values
vacation1 = "Summer Vacation"
vacation2 = "Winter Vacation"

For example, reference the code in vacations.py above in the script below.

# Import another python script
import vacations as v
# Initialize the month list
months = ["January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"]
# Initial flag variable to print summer vacation one time
flag = 0
# Iterate the list using for loop
for month in months:
if month == "June" or month == "July":
if flag == 0:
print("Now",v.vacation1)
flag = 1
elif month == "December":
print("Now",v.vacation2)
else:
print("The current month is",month)

6. List comprehension

Python list comprehension is a method to quickly and concisely create data types from one or more iterators. It combines loops and conditional judgments, thus Avoid code with lengthy syntax and improve code running efficiency. Being able to use derivation proficiently can also indirectly indicate that you have surpassed the level of Python beginners.

# Create a list of characters using list comprehension
char_list = [ char for char in "linuxhint" ]
print(char_list)
# Define a tuple of websites
websites = ("google.com","yahoo.com", "ask.com", "bing.com")
# Create a list from tuple using list comprehension
site_list = [ site for site in websites ]
print(site_list)

7. Reading and writing files

One of the most commonly used scenarios for interactive Python with calculations is to read the CSV file in the D drive, then rewrite the data and save it. This requires Python to perform operations of reading and writing files, which is also a core skill that beginners need to master.

#Assign the filename
filename = "languages.txt"
# Open file for writing
fileHandler = open(filename, "w")
# Add some text
fileHandler.write("Bashn")
fileHandler.write("Pythonn")
fileHandler.write("PHPn")
# Close the file
fileHandler.close()
# Open file for reading
fileHandler = open(filename, "r")
# Read a file line by line
for line in fileHandler:
print(line)
# Close the file
fileHandler.close()

8. Slicing and indexing

Sequences in the form of lists, strings, tuples, etc. all have the need for slicing and indexing, because we need to intercept data from them, so this is also very core. skills.

var1 = 'Hello World!'
var2 = "zhihu"
print ("var1[0]: ", var1[0])
print ("var2[1:5]: ", var2[1:5])

9、使用函数和类

函数和类是一种封装好的代码块，可以让代码更加简洁、实用、高效、强壮，是python的核心语法之一。

定义和调用函数。

# Define addition function
def addition(number1, number2):
result = number1 + number2
print("Addition result:",result)
# Define area function with return statement
def area(radius):
result = 3.14 * radius * radius
return result
# Call addition function
addition(400, 300)
# Call area function
print("Area of the circle is",area(4))

定义和实例化类。

# Define the class
class Employee:
name = "Mostak Mahmud"
# Define the method
def details(self):
print("Post: Marketing Officer")
print("Department: Sales")
print("Salary: $1000")
# Create the employee object
emp = Employee()
# Print the class variable
print("Name:",emp.name)
# Call the class method
emp.details()

10、错误异常处理

编程过程中难免会遇到错误和异常，所以我们要及时处理它，避免对后续代码造成影响。

所有的标准异常都使用类来实现，都是基类Exception的成员，都从基类Exception继承，而且都在exceptions模块中定义。

Python自动将所有异常名称放在内建命名空间中，所以程序不必导入exceptions模块即可使用异常。一旦引发而且没有捕捉SystemExit异常，程序执行就会终止。

异常的处理过程、如何引发或抛出异常及如何构建自己的异常类都是需要深入理解的。

# Try block
try:
# Take a number
number = int(input("Enter a number: "))
if number % 2 == 0:
print("Number is even")
else:
print("Number is odd")
# Exception block
except (ValueError):
# Print error message
print("Enter a numeric value")

小结

当然Python还有很多有用的函数和方法，需要大家自己去总结，这里抛砖引玉，希望能帮助到需要的小伙伴。

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