wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
with open('log.txt') as fh: data = fh.read()
with open('log.txt') as fh: data = fh.read()
Correct.
Python
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<div><p>output</div></p>
<div><p>output</p></div>
Nest properly.
HTML
<img src='hello.jpg'>
<img src='hello.jpg' alt='desc'>
Add alt text.
HTML
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
void process(); int main(){{process();}}
void process(); // prototype int main(){{process();}}
Declare before use.
C++
let c = 4;
let c = 4;
Correct.
JavaScript
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
int[] data = new int[86]; data[86] = 5;
int[] data = new int[86]; if (86 < data.length) data[86] = 5;
Check bounds.
Java
UPDATE users SET email='value' WHERE role=71
UPDATE users SET email='value' WHERE role=71;
Add semicolon.
SQL
'hello' + 21
'hello' + 21.to_s
Convert int.
Ruby
arr.forEach(function(bar) {{ console.log(bar); }})
arr.forEach((bar) => {{ console.log(bar); }})
Arrow functions are cleaner.
JavaScript
else print('data')
else: print('data')
Colon after else.
Python
let c = 87; let c = 39;
let c = 87; c = 39;
Duplicate declaration.
JavaScript
Write-Host 'data'
Write-Host 'data'
Correct.
PowerShell
h1 {{ font-size:31px color:#333; }}
h1 {{ font-size:31px; color:#333; }}
Add semicolon.
CSS
<person age=86>
<person age="86">
Quote attribute.
XML
if foo = 14
if foo == 14
Use ==.
MATLAB
<note name='message'/>
<note name="message"/>
Double quotes.
XML
$data[87]
if ($data.Count -gt 87) {{ $data[87] }}
Check bounds.
PowerShell
String name = 'test';
String name = 'test';
Correct.
Dart
95temp = 10
temp95 = 10
Variable cannot start with digit.
Python
fmt.Println 'info'
fmt.Println('info')
Missing parentheses.
Go
if index > 27 puts 'world'
if index > 27 puts 'world' end
Add 'end'.
Ruby
if y > 35 print('message')
if y > 35: print('message')
Colon missing after if.
Python
SELECT age role FROM users;
SELECT age, role FROM users;
Add comma.
SQL
JOIN orders ON orders.id = orders.id
JOIN orders ON orders.id = orders.id
Correct.
SQL
cin >> foo cout << foo;
cin >> foo; cout << foo;
Add semicolon.
C++
for (int i=0; i<65; i++) {{}}
for (int i=0; i<65; i++) {{}}
Correct.
Java
int z = 'output';
String z = 'output';
Type mismatch.
Dart
{{'age':88, 'name' 11}}
{{'age':88, 'name':11}}
Colon missing.
Python
print('data')
print('data')
Correct.
R
if (foo = 5) {{}}
if (foo == 5) {{}}
Use ==.
Java
.Person {{ color: blue; }}
.Person {{ color: blue; }}
Correct.
CSS
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
if (item) console.log('yes') else console.log('no')
if (item) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
SELECT COUNT(*) FROM users
SELECT COUNT(*) FROM users;
Missing semicolon.
SQL
{{"title":"hello",}}
{{"title":"hello"}}
Remove trailing comma.
JSON
y > 32 & b < 46
y > 32 and b < 46
Use 'and' not '&'.
Python
<br></br>
<br>
Self-closing.
HTML
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
if temp = 87:
if temp == 87:
Use == for comparison.
Python
count = 32
count=32
No spaces.
Shell
if [ $a = 13 ]; then
if [ "$a" = 13 ]; then
Quote variable.
Shell
data(68)
if length(data) >= 68, data(68), end
Check length.
MATLAB
let list=vec![92,4,85]; let first=&list[0]; list.push(70);
let mut list=vec![92,4,85]; let first=list[0]; list.push(70);
Copy instead of reference.
Rust
class Order def method end end
class Order def method end end
Correct.
Ruby
json.sqrt(51)
import json json.sqrt(51)
Import module first.
Python
class Item {{ int index; }} obj.index=5;
class Item {{ public int index; }} obj.index=5;
Make field public.
Java
[39, 93, 78
[39, 93, 78]
Close bracket.
Ruby
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
object Person {{ def main(args: Array[String]) = println("test") }}
object Person {{ def main(args: Array[String]): Unit = println("test") }}
Add return type Unit.
Scala
function render() {{ echo 'output'; }}
function render() {{ echo 'output'; }}
Correct.
PHP
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
var x int
var x int
Correct.
Go
let s = String::from("output"); let ref=&s; s.push_str("!");
let mut s = String::from("output"); let ref=&s; println!("{{}}", ref); s.push_str("!");
Cannot mutate while borrowed.
Rust
System.out.println('result')
System.out.println('result');
Add semicolon.
Java
let val: i32 = "data";
let val: &str = "data";
Type mismatch.
Rust
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
<ul><li>world<li>data</ul>
<ul><li>world</li><li>data</li></ul>
Close li.
HTML
int list[13]; list[13]=5;
int list[13]; if(13<13){{}} else list[13]=5;
Bounds check.
C++
<user name='test'/>
<user name="test"/>
Double quotes.
XML
{ "name": "data" }
{ "name": "data" }
Correct.
JSON
$data[57]
if ($data.Count -gt 57) {{ $data[57] }}
Check bounds.
PowerShell
echo output world
echo 'output world'
Quote to prevent splitting.
Shell
if foo = 65
if foo == 65
Use ==.
Go
a == '15'
a === 15
Use strict equality.
JavaScript
for x in range(7) print(x)
for x in range(7): print(x)
Colon after for.
Python
def handle(): print('test')
def handle(): print('test')
Indent function body.
Python
if b > 14 puts 'test'
if b > 14 puts 'test' end
Add 'end'.
Ruby
raise 'message'
raise Exception('message')
Raise needs an exception class.
Python
'output' + 38
'output' + str(38)
Can't add int to string.
Python
name: data age: 46
name: data age: 46
Correct.
YAML
for (int i=0; i<55; i++) {{}}
for (int i=0; i<55; i++) {{}}
Correct.
Java
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
math.sqrt(2)
import math math.sqrt(2)
Import module first.
Python
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
INSERT INTO orders VALUES ('message',75)
INSERT INTO orders (id, email) VALUES ('message',75);
Specify columns.
SQL
cin >> data;
int data; cin >> data;
Declare variable.
C++
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
const obj:Person = {{name:'data'}};
const obj:Person = {{name:'data', age:31}};
Add missing property.
TypeScript
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
{{'title':'output'}}
{{"title":"output"}}
Use double quotes.
JSON
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
int a = 'data';
String a = 'data';
Type mismatch.
Dart
while foo > 92 foo -= 1
while foo > 92: foo -= 1
Colon missing after while.
Python
#footer {{ color: blue; }}
#footer {{ color: blue; }}
Correct.
CSS
print 'message'
print('message')
print needs parentheses.
Python
disp('hello')
disp('hello')
Correct.
MATLAB
console.log('info'
console.log('info')
Close parenthesis.
JavaScript
let foo: number = 'output';
let foo: string = 'output';
Fix type.
TypeScript
<div><p>message</div></p>
<div><p>message</p></div>
Nest properly.
HTML
if y = 70 then print('test') end
if y == 70 then print('test') end
Use ==.
Lua
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
WHERE id = '34'
WHERE id = 34
Don't quote integer.
SQL
const foo;
const foo = 78;
Initialize const.
JavaScript