Python is none invalid syntax

invalid syntax error in Python [How to fix with examples]

In this Python tutorial, we will discuss everything about invalid syntax Python. We will see, when “syntaxerror: invalid syntax” error appears in Python. And also how to fix invalid syntax error in Python.

Why invalid syntax error in Python?

An invalid syntax error in Python can appear for a multitude of reasons, some of which are:

1. Misspelled Keywords: Python has a set of reserved keywords that should be spelled correctly. For instance, typing ‘fro’ instead of ‘for’ will result in a syntax error.
2. Improper Indentation: Python uses indentation to differentiate between blocks of code. If your code is not indented correctly, Python will throw an error.
3. Incorrect Punctuation: Each statement in Python must end with a newline. If a statement is broken up incorrectly or punctuation such as colons and parentheses are misplaced, it can result in a syntax error.
4. Variable Names: If a variable name starts with a number or contains spaces or special characters (with the exception of underscores), it’s going to be a problem for Python.
5. Incorrect Function Calls: If functions are called without the correct number or type of arguments, Python will throw an error.

How to fix invalid syntax in Python

Here are a few examples, that we can follow to fix invalid syntax in Python.

Example 1: Misspelled Keywords

In the code above, ‘for’ is misspelled as ‘fro’, which results in a SyntaxError. Check out the output below:

Simply correcting the spelling of ‘for’ fixes the issue.

Example 2: Improper Indentation

Python uses indentation to indicate blocks of code. In the code above, the ‘print’ statement isn’t indented correctly and hence Python raises a SyntaxError.

By indenting the ‘print’ statement correctly under the function definition, the syntax error is resolved.

Example 3: Incorrect Punctuation

The ‘if’ statement is missing a colon at the end which causes a SyntaxError. You can see the output when you run the code like below:

Adding the missing colon resolves the syntax error.

Example 4: Incorrect Variable Names

Variable names in Python cannot begin with a number. The above line will therefore raise a SyntaxError.

By changing the variable name to start with a character, the syntax error is resolved.

Example 5: Incorrect Function Calls

print("Hello, World!", end = " ", "Goodbye, World!")

The print function does not accept multiple string arguments after a keyword argument. The above code will therefore raise a SyntaxError.

print("Hello, World!", end = " ") print("Goodbye, World!")

Splitting the print statements into two corrects the issue.

Remember, the key to fixing syntax errors is carefully reading the error messages and understanding what Python is struggling to understand. With practice, you’ll find these become easier to spot and correct. I hope you can now fix the invalid syntax error in Python.

I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.

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Что означает ошибка SyntaxError: invalid syntax

Ситуация: программист взял в работу математический проект — ему нужно написать код, который будет считать функции и выводить результаты. В задании написано:

«Пусть у нас есть функция f(x,y) = xy, которая перемножает два аргумента и возвращает полученное значение».

Программист садится и пишет код:

a = 10 b = 15 result = 0 def fun(x,y): return x y result = fun(a,b) print(result)

Но при выполнении такого кода компьютер выдаёт ошибку:

File «main.py», line 13
result = x y
^
❌ SyntaxError: invalid syntax

Почему так происходит: в каждом языке программирования есть свой синтаксис — правила написания и оформления команд. В Python тоже есть свой синтаксис, по которому для умножения нельзя просто поставить рядом две переменных, как в математике. Интерпретатор находит первую переменную и думает, что ему сейчас объяснят, что с ней делать. Но вместо этого он сразу находит вторую переменную. Интерпретатор не знает, как именно нужно их обработать, потому что у него нет правила «Если две переменные стоят рядом, их нужно перемножить». Поэтому интерпретатор останавливается и говорит, что у него лапки.

Что делать с ошибкой SyntaxError: invalid syntax

В нашем случае достаточно поставить звёздочку (знак умножения в Python) между переменными — это оператор умножения, который Python знает:

a = 10 b = 15 result = 0 def fun(x,y): return x * y result = fun(a,b) print(result)

В общем случае найти источник ошибки SyntaxError: invalid syntax можно так:

1. Проверьте, не идут ли у вас две команды на одной строке друг за другом.
2. Найдите в справочнике описание команды, которую вы хотите выполнить. Возможно, где-то опечатка.
3. Проверьте, не пропущена ли команда на месте ошибки.

Практика

Попробуйте найти ошибки в этих фрагментах кода:

x = 10 y = 15 def fun(x,y): return x * y

try: a = 100 b = "PythonRu" assert a = b except AssertionError: print("Исключение AssertionError.") else: print("Успех, нет ошибок!")

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Python Null | What is Null in Python | None in Python

In Python, there is no null keyword or object available. Instead, you may use the ‘None’ keyword, which is an object.

We can assign None to any variable, but you can not create other NoneType objects.

Note: All variables that are assigned None point to the same object. New instances of None are not created.

Syntax

The syntax of None statement is:

This is how you may assign the ‘none’ to a variable in Python:

We can check None by keyword “is” and syntax “==”

Null Object in Python

In Python, the ‘null‘ object is the singleton None .

The best way to check things for “Noneness” is to use the identity operator, is :

Note: The first letter in ‘None’ keyword is the capital N. The small ‘n’ will produce an error.

In other programming languages, for example, this is how you may create a null variable in PHP and Java.

Null in Java

Null in PHP

If you need to evaluate a variable in the if condition, you may check this as follows in Java:

How to use the ‘None’ in Python. I will use it in the if statement and a few compound data types.

Checking if a variable is None (Null) in Python using is operator:

# Declaring a None variable var = None if var is None: # Checking if the variable is None print("None") else: print("Not None")

Python Null Using the == operator

Rather than using the identity operator in the if statement, you may also use the comparison operators like ==, != etc. for evaluating a ‘none’ value. See the example with the code below where the same code is used as in the above example except the comparison operator:

#A demo of none variable with == operator ex_none = None if ex_none == None: print('The value of the variable is none') else: print('Its a not null variable')

The output of the above example is:

The value of the variable is none

None (Null) value in a List example

Similarly, you may use the Null value in the compound data type List. Just use the None keyword as in case of sets.

See this example where I have created a list and the third item in the list is None keyword:

# An example of a List with None str_list_None = ['List','with', None, 'Value'] for str in str_list_None: print ("The current list item:",str)

Using None(Null) for default args in Python

Using anything but None for default, arguments make objects and functions less extensible.

we’re going to use None for our default argument, subbing in our default value when none is provided:

DEFAULT_FOOD = 'catfood' class Cat: def eat(self, food=None): if food is None: food = DEFAULT_FOOD return food cat = Cat() cat.eat() # catfood cat.eat('tuna') # tuna

Our class still behaves the same but is easier to extend. Look how we no longer need to worry about the default value constant in our Tabby to maintain the same method signature:

Check the type of None (Null) object:

# Declaring a variable and initializing with None type typeOfNone = type(None) print(typeOfNone)

Check if None is equal to None

# Python program to check None value # initialized a variable with None value myval = None if None is None: print('None is None') else: print('None is Not None') print(None == None)

Check if None is equal to an empty string

# Inilised a variable with None value myval = '' if myval == None: print('None is equal to empty string') else: print('None is Not Equal to empty string') print(None == myval)

Output

None is Not Equal to empty string False

Assigning a NULL value to a pointer in python

In Python, we use None instead of NULL. As all objects in Python are implemented via references, See the code below:-

class Node:

def __init__(self):

self.val = 0

self.right = None

self.left = None

None cannot be overwritten

In a much older version of Python (before 2.4) it was possible to reassign None , but not anymore. Not even as a class attribute or in the confines of a function.

# In Python 2.7 >>> class SomeClass(object): . def my_fnc(self): . self.None = 'foo' SyntaxError: cannot assign to None >>> def my_fnc(): None = 'foo' SyntaxError: cannot assign to None # In Python 3.5 >>> class SomeClass: . def my_fnc(self): . self.None = 'foo' SyntaxError: invalid syntax >>> def my_fnc(): None = 'foo' SyntaxError: cannot assign to keyword

It’s, therefore, safe to assume that all None(Null) references are the same. There’s no “custom” None .

Difference between Null and empty string in Python

Python doesn’t have a Null string at all.

Python does have a None value but it isn’t a string it is A None that can be applied to all variables – not just those which are originally defined as a string. In fact, Python doesn’t care what a variable has been defined as previously – this is entirely valid code (although not a great idea):

data=23 data = [23,24,25,26,27] # Now a list date = ‘Hello World’ # Now a string data = None

So to try to answer your question

date = None

A Null or empty string means that there is a string but its content is empty –

len(‘ ’) ==0. For Python, the term ‘Empty string’ is preferred.

Image Explains it all

This image shows a clear difference between Non-Zero, 0, null and undefined.

Conclusion

None has a distinctive status in Python language. It’s a preferred baseline value because many algorithms treat it as an exceptional value.

In such scenarios, it can be used as the flag to signal that the condition requires some special handling such as the setting of the default value.

If you didn’t find what you were looking, then do suggest us in the comments below. We will be more than happy to add that.

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