Python data entry with multiple lines

Question

I would like to understand how to input several data (int, float, str...) per line but repeatedly (i.e., in several lines) so that I can save each given input.

I understand that I will have to use a list to store each input and, using split, I can input several data on the same line, but I get lost when it comes to doing this with several lines.

For example:

linha = input().split()

lista = []
for item in range(5):
    x = int(linha[item])
    lista.append(x)
print(lista)

This code gives me a line with several input data (integers), I would like to repeat this process in as many lines as I want and with the various types of data I want. However, as a beginner, I’m still not used to the syntax.

Answer 1

The function input() always returns a string, to work with other types of data we need to manipulate this string, so let’s go by parts.

---

Receive multiple values

We can solve this problem with different approaches, example:

Getting all values at once.

We can receive a string with all values separated by whitespace and use the method str.split() to "break" this string into a list of strings. Example:

linha = input("Digite os valores separados por espaço")
# ex.: '1 2 3 4 5'
valores = linha.split()
# ['1', '2', '3', '4', '5']

If you want to convert all values to integer you can use:

• A for to iterate on the values, convert the value and then add to the result list with list.append().

  linha = input("Digite os valores separados por espaço")
  valores = []
  
  for valor in linha.split():
      valores.append(int(valor))
  

• The function map to apply a function to all items of an iterable and create a new list with the function result for each position of the list.

  linha = input("Digite os valores separados por espaço")
  valores = linha.split()
  valores_convertidos = map(int, valores)
  

• One comprehensilist on to iterate and convert all values:

  linha = input("Digite os valores separados por espaço")
  valores = linha.split()
  valores_convertidos = [int(valor) for valor in valores]
  

Receiving one value at a time

You can receive an indefinite number of inputs using a loop and setting a stop criterion.

For example, receive integer numbers while the user enters valid values:

valores = []

while True:
    try:
        linha = int(input("Digite um número:"))
    except ValueError:
        print("Valor inválido, saindo do loop")
        break

    valores.append(linha)

In the above code I am creating an "infinite" loop that will be repeated while converting user input to int not fail. When it fails it will launch a ValueError running the break within the except

---

Receiving a specific number of variables with predefined types

You can receive a specific number of inputs using the function range() as you yourself posted in your question:

valores = []

for _ in range(5):
    valor = input("Digite algo: ")
    valores.append(valor)

The next step is to define the types of data we should receive. We could use whole numbers or even strings to define data types.

Example:

# 0: int
# 1: str
# 2: float
tipos = [0, 1, 1, 0, 2]
valores = []

for tipo in tipos:
    valor = input("Digite algo: ")

    if tipo == 0:
        valores.append(int(valor))
    elif tipo == 1:
        valores.append(valor)  # já é string
    elif tipo ==2:
        valores.append(float(valor))
    else:
        print("Tipo inválido, nenhum valor adicionado")

I won’t go into too much into the improvements that could be made in the above code as it is only a demonstration of how it could be done.

Instead of having several if for each type you would like to have, you could use a list of functions that receive a string and return the type you want. In python, functions are "first-class citizens", this means that you can pass them as parameters to other functions, assign them to variables, etc...

So it’s possible to do something like:

meu_int = int
valor = meu_int("10")
print(valor)  # 10

Applying this concept, remaking the example and removing the if would be:

tipos = [int, str, str, int, float]
valores = []

for tipo in tipos:
    valor = input("Digite algo: ")
    valores.append(tipo(valor))

^{Code running on Repl.it}

This way you are specifying that you want the user to enter 5 values, namely an integer, 2 strings, 1 integer and 1 float, respectively. Not to mention that you can create your own functions or classes that receive a string as input and return an object of the type you want.

Completion

As the subject is generic, it turned out that the answer got a little wide, but the important thing is that you understand that there are several approaches to the same problem and I hope to have given enough material for you to have a starting point for new studies and new questions.

Answer 2

Abuse and use of try

texto = '''1
teste
1.5
balb
512

1,4'''
# Separa String por linhas e cria uma lista
lst = texto.split('\n')

lst_tratada = []
# Para cada valor que estiver na lista
for i in lst:
    # Tenta registrar o valor como int e vai para o próximo laço, senão continua
    try:
        lst_tratada.append(int(i))
        continue
    except:
        pass
    # Tenta registrar o valor como float e vai para o próximo laço, senão continua
    try:
        lst_tratada.append(float(i))
        continue
    except:
        # Se não conseguir nenhum dos dois, tratar como string
        lst_tratada.append(i)

print(lst_tratada)

A simpler approach, from a method:

def var_parser(x):
    try: # Tenta retornar x como inteiro
        return int(x)
    except: # Se não obtiver exito, continuar
        pass
    try: # Tenta retornar x como float
        return float(x)
    except: # Se não obtive exito, retornar x 
        return x


texto = '''1
teste
1.5
balb
512

1,4'''

lst = texto.split('\n')

lst_tratada = []
for i in lst:
    lst_tratada.append(var_parser(i))

print(lst_tratada)