AttributeError

AttributeError: XXX object has no attribute YYY

An attempt was made to apply a method (indicated by YYY) to the object XXX but the method does not exist for the type of XXX. A particular case occurs when a module is imported with the import statement and an attempt is made to call a function of this module that does not exist in the file.

Examples

In this example, an attempt is made to apply the replace method to a list but this method does not exist for this type.

def canvia_0_per_1(llista):
    i=0
    for i in range(len(llista)):
        if llista[i]==0:
            llista = llista.replace(0,1)
    

>>> lnum = [0,2,5,0,2,0]
>>> objecthasnoattribute1.canvia_0_per_1(lnum)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "objecthasnoattribute1.py", line 5, in canvia_0_per_1
    llista = llista.replace(0,1)
AttributeError: 'list' object has no attribute 'replace'

In this example filename is a string parameter that contains the name of a file. The notation filename.txt contains a string object followed by a dot and, therefore, is interpreted by Python as a call to the txt method which must be a string method, but this method does not exist and gives an error.

def cost_total(nomfitxer):
    f = open(nomfitxer.txt,'r')
    ctotal = 0
    for linia in f:
        ldades = linia.split()
        unitats = int(ldades[1])
        cost = float(ldades[2])
        ctotal = ctotal + unitats * cost 
    f.close()
    return ctotal

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "objecthasnoattribute2.py", line 2, in cost_total
    f = open(nomfitxer.txt,'r')
AttributeError: 'str' object has no attribute 'txt'

This example corresponds to the particular case mentioned above. The inventory module is imported and then the module function called total is called. The error indicates that there is no function in the ``inventory.py

>>> import inventari
>>> inventari.total()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'total'

FileNotFoundError

FileNotFoundError: [Errno 2] No such file or directory: XXX

An attempt was made to open a file named XXX for reading that does not exist.

Example

In this example, line 2 attempts to open the file inventario.txt for reading, but Python cannot find this file. Often the problem is that it is not the correct name or the file is not in the directory (folder) where we are located.

def cost_total():
    f = open('inventari.txt','r')
    ctotal = 0
    for linia in f:
        ldades = linia.split()
        unitats = int(ldades[1])
        cost = float(ldades[2])
        ctotal = ctotal + unitats * cost 
    f.close()
    return ctotal

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "filenotfound1.py", line 2, in cost_total
    f = open('inventari.txt','r')
FileNotFoundError: [Errno 2] No such file or directory: 'inventari.txt'

ImportError

ImportError: No module named XXX

An attempt was made to import a module named XXX.py* but no file with this name exists.

Example

In this example, we try to import the conversions.py module but it gives an error because Python cannot find this file. Often the problem lies in the fact that it is not the correct name or the file is not in the directory (folder) where we are located.

>>> import conversions
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named 'conversions'

IndentationError

IndentationError: expected an indented block

There are missing spaces in front of a statement that goes inside a code block in an if, while, for, etc.

Example

In this example, the statement that must be executed if the condition is met cannot go at the same height as the if.

def descompte1(imp,iva):
    total = imp + imp*iva/100.0
    if total > 100:
    total = total -5
    return total

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "expectindent1.py", line 4
    total = total -5
        ^
IndentationError: expected an indented block

IndentationError: unexpected indent

Excess spaces before a statement.

Example

In this example, line 3 has more spaces than necessary and should be at the height of the previous line.

def descompte1(imp,iva):
    total = imp + imp*iva/100.0
      total = total -5
    return total

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "unexpectindent1.py", line 3
    total = total -5
    ^
IndentationError: unexpected indent

IndentationError: unindent does not match any outer indentation level

The spacing of a statement does not match any spacing level of the others.

Example

In this example, the statement on line 4 is not aligned with either line 1 or line 2 or 3. In this case, it should have one more space.

def descompte1(imp,iva):
    total = imp + imp*iva/100.0
    total = total -5
   return total

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "unindentdoesnotmatch1.py", line 4
    return total
               ^
IndentationError: unindent does not match any outer indentation level

IndexError

IndexError: XXX index out of range

An attempt was made to access the position of a value (of the type indicated by XXX) using an index that is not within the allowed range.

Example

In this example, the function receives the string text as a parameter and assigns the length of this string to the variable ultima (line 2). Later (line 3) an attempt is made to access the position indicated by ultima which is outside the allowed range and gives an error. The indices of a string start from 0 and so the maximum allowed index is the length minus 1.

def igualprimeraultima(text):
    ultima = len(text)
    if text[0] == text[ultima]:
        return 'iguals'
    else:
        return 'diferents'
    

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "indexoutrange1.py", line 3, in igualprimeraultima
    if text[0] == text[ultima]:
IndexError: string index out of range

KeyError

KeyError: XXX

An attempt was made to access a value in a dictionary through the key XXX but this key does not exist.

Example

In this example, the keys of the dictionary are the strings ‘BUS’, ‘BICING’ and ‘METRO’ and therefore the attempt to access through the key 12 gives an error.

>>> d = {'BUS':23,'BICING':35,'METRO':12}
>>> d[12]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 12

NameError

NameError: name XXX is not defined

A reference was made to a name (indicated by XXX) that Python does not know because it is not in the language or has not been defined.

Exemples

Calling a function with a different name than the one used in the definition. In this case, the call convseconds is incorrect because we have defined the function as conv_seconds.

def conv_segons(h,m,s):
    segons = h*3600+m*60+s
    return segons

>>> from conversions import *
>>> convsegons(1,3,40)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'convsegons' is not defined

Using functions from an external module that has not been imported. In this case, the call to the sin function is incorrect because this function is in the math module and has not been imported. Once imported and called correctly, it works.

>>> sin(1.57)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'sin' is not defined
>>> import math
>>> math.sin(1.57)
0.9999996829318346

SyntaxError

SyntaxError: invalid syntax

The syntax does not conform to Python writing rules.

Exemples

Using operators incorrectly. In this case, the expression that calculates 2 multiplied by the variable k is incorrect because the multiplication operator * is missing.

def f(x,k):
    num = 1 /(2*x+1)
    y = num/(2k-1)
    res = num/y
    return y

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "invalidsyntax1.py", line 3
    y = num/(2k-1)
              ^
SyntaxError: invalid syntax

Use = instead of == to make comparisons.

def es_parell(n):
    if n%2 = 0:
        return True
    else:
        return False

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "invalidsyntax2.py", line 2
    if n%2 = 0:
           ^
SyntaxError: invalid syntax

Not writting : at the end of the statements that require it (if, elif, else, for, while, def). In this example, they need to be put at the end of the if statement.

def es_parell(n):
    if n%2 == 0
        return True
    else:
        return False

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "invalidsyntax3.py", line 2
    if n%2 == 0
              ^
SyntaxError: invalid syntax

Use a Python reserved word as a variable name (in this example in)

def celsius_kelvin(c):
    in = c + 273.15
    return in

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "invalidsyntax4.py", line 2
    in = c + 273.15
     ^
SyntaxError: invalid syntax

SyntaxError: EOL while scanning string literal

Missing quotes (single or double, depending on the code) to open or close a string.

Example

En aquest exemple falta tancar la cometa de l´últim string a la línia 2.

def genera_adreca(nom,cognom):
    s = nom + '.' + cognom + '@estudiant.upc.edu
    return s

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "eolscanning1.py", line 2
    s = nom + '.' + cognom + '@estudiant.upc.edu
                                               ^
SyntaxError: EOL while scanning string literal

SyntaxError: EOF while scanning triple-quoted string literal

Example

def genera_adreca(nom,cognom):
    """
    >>> genera_adreca('pep','pepot')
    'pep.pepot@estudiant.upc.edu'
    
    s = nom + '.' + cognom + '@estudiant.upc.edu'
    return s

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "eolscanningtriple1.py", line 7
    return s
           ^
SyntaxError: EOF while scanning triple-quoted string literal

TypeError

TypeError: Can’t convert XXX object to str implicitly

An attempt was made to use a string operation with some other data type (indicated by XXX)

Example

In this example, line 4 tries to concatenate an integer to the variable s that contains a string.

def afegeix_bin(num):
    s = '00'
    if num >= 0:
        s = s + 1
    else:
        s = s + '0'
    return s

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "cantconvertstr1.py", line 3, in afegeix_bin
    s = s + 1
TypeError: Can't convert 'int' object to str implicitly

TypeError: unorderable types: XXX > YYY

An attempt was made to compare two different types (XXX and YYY indicate the types) that cannot be compared because they are not ordered between them.

Example

In this example the variable prod_code contains a string and an attempt is made to compare with an integer.

>>> codi_prod = '2'
>>> codi_prod > 0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unorderable types: str() > int()

TypeError: can only concatenate XXX (not YYY) to XXX

An attempt was made to concatenate values ​​of two different types (indicated by XXX and YYY).

Example

In this example, the intersection function has been executed with the values ​​``list1=[1,2,3]`` and list2=[2,3,4,5]. On line 5, an attempt is made to concatenate to the variable lres, which is a list, a value from list1 that is an integer.

def interseccio(llista1,llista2):
    lres = []
    for c in llista1:
        if c in llista2:
            lres = lres + c
    return lres

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "canonlyconcat1.py", line 5, in interseccio
    lres = lres + c
TypeError: can only concatenate list (not "int") to list

TypeError: XXX indices must be integers, not YYY

An attempt was made to access an element of an indexed type (such as a list)

Example

This example attempts to access a position in a string using another string. When an integer is used (in this case 12) the access is executed correctly.

>>> s = "Fonaments d'Informàtica"
>>> s['I']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: string indices must be integers
>>> s[12]
'I'

TypeError: unsupported operand type(s) for XXX: YYY and ZZZ

An attempt was made to apply an operator (indicated by XXX) to values ​​of a type that does not accept this type of operation (indicated by YYY and ZZZ).

Exemples

In these examples, an attempt is made to apply numeric type operands (division, addition, and subtraction) to types that do not accept this type of operation such as strings or lists.

>>> s1 = '3'
>>> s2 = '7'
>>> s1/s2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'str' and 'str'
>>> s1-2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'str' and 'int'
>>> l = [2, 4, 5]
>>> 3.56+l
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'float' and 'list'

TypeError: bad operand type for unary XXX: YYY

An attempt was made to apply a unary operator (indicated by XXX) to a value that does not accept this type of operation (indicated by YYY).

Example

This example applies the sign change operation to a string, a type that does not accept this operation.

>>> s = '3'
>>> -s
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bad operand type for unary -: 'str'

TypeError: XXX object is not subscriptable

An attempt was made to access an element through an index to a value of a type (indicated by XXX) that does not accept indexing, or an attempt was made to obtain a slice of a type that does not accept the operation.

Example

In this example, the values ​​taken by the variable i are integers, since they are generated from the for-in-range statement. On line 4 of the function, an attempt is made to access position 0 of the variable i, which gives an error because integers cannot be indexed.

def comenca_vocal(llista):
    n = 0
    for i in range(len(llista)):
        if i[0] in 'AEIOUaeiou':
            n = n + 1
    return n

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "objectnotsubscript1.py", line 4, in comenca_vocal
    if i[0] in 'AEIOUaeiou':
TypeError: 'int' object is not subscriptable

TypeError: XXX missing YYY required positional argument: ZZZ

An attempt was made to call the function (indicated by XXX) with fewer parameters (indicated by YYY) than required. The name of the parameters is indicated by ZZZ.

Example

In this example, the conv_segons function is defined with three parameters but the call is only given two.

def conv_segons(h,m,s):
    segons = h*3600+m*60+s
    return segons

>>> import conversions
>>> conversions.conv_segons(1,5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: conv_segons() missing 1 required positional argument: 's'
>>> 

TypeError: XXX object cannot be interpreted as an YYY

A value or variable of type XXX has been used in a context where type YYY is required.

Example

In this example, on line 3, the range function requires an integer parameter and has been passed a list, instead of the length of the list, which is an integer.

def suma_llista(l):
    s = 0
    for i in range(l):
        s = s + l[i]
    return s

>>> import cannotbeinterpreted
>>> cannotbeinterpreted.suma_llista([1,2,3])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "cannotbeinterpreted.py", line 3, in suma_llista
    for i in range(l):
TypeError: 'list' object cannot be interpreted as an integer

TypeError: unhashable type: XXX

An attempt was made to use the data type XXX which is not immutable as a key in a dictionary.

Example

In this example, a dictionary is defined where the keys are tuples, but an attempt is made to check if a key exists that is a list, which is a mutable type and gives an error.

>>> d = {(1,2):'vermell',(5,5):'blau',(3,7):'blau'}
>>> llista = [2,3]
>>> llista in d
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>> 

UnboundLocalError

UnboundLocalError: local variable xxx referenced before assignment

Inside a function, an attempt was made to access the value of a variable that has not been defined before.

Example

In this example, no value has been given to the variable com and an attempt has been made to access its value on line 3.

def comissions(dep,pref):
    if dep > 500000:
        com = com + dep * 0.005
    if pref > 500000:
        com = com + pref * 0.03
    return com

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "localvarrefbefore1.py", line 3, in comissions
    com = com + dep * 0.005
UnboundLocalError: local variable 'com' referenced before assignment

ValueError

ValueError: could not convert XXX to YYY: ZZZ

An attempt has been made to convert from type XXX to type YYY with the value ZZZ, but the value does not have a suitable format for the conversion.

Example

In this example, an attempt is made to convert the string s to a real number, but since it contains a comma, the conversion cannot be carried out, since Python uses the dot to denote decimals and the float function does not know how to interpret the string as a real number. A string containing a dot is then assigned to it and the conversion is performed without problems.

>>> s = '276,25'
>>> float(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '276,25'
>>> s = '276.25'
>>> float(s)
276.25

ValueError: invalid literal for int() with base 10: XXX

An attempt was made to convert the value XXX to integer but this value does not have a suitable format in base 10.

Example

In this example the string s contains a period and therefore the format is incorrect as an integer. Later it is shown how when executing the conversion to float it does work, since the format is correct as a real, or if the string is assigned a value with only integers, the conversion to integer is also executed correctly.

>>> s = '276.25'
>>> float(s)
276.25
>>> s = '125.12'
>>> int(s)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '125.12'
>>> float(s)
125.12
>>> s = '125'
>>> int(s)
125

ValueError: math domain error

An attempt was made to execute a mathematical operation with incorrect data.

Example

In this example, we try to call the function f with the value 0 for the parameter x, which, within the function, tries to calculate the square root of -1 and gives an error because it is a negative number.

import math

def f(x):
    return math.sqrt(x-1)+math.sin(x)

>>> import funcio
>>> funcio.f(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "funcio.py",line 4, in f
    return math.sqrt(x-1)+math.sin(x)
ValueError: math domain error