Convert numpy, list or float to string in python

问题:

I'm writing a python function to append data to text file, as shown in the following,

The problem is the variable, var, could be a 1D numpy array, a 1D list, or just a float number, I know how to convert numpy.array/list/float to string separately (meaning given the type), but is there a method to convert var to string without knowing its type?

def append_txt(filename, var):     my_str = _____    # convert var to string     with open(filename,'a') as f:         f.write(my_str + '\n') 

Edit 1: Thanks for the comments, sorry maybe my question was not clear enough. str(var) on numpy would give something like []. For example, var = np.ones((1,3)), str(var) will give [[1. 1. 1.]], and [] is unwanted,

Edit 2: Since I want to write clean numbers (meaning no [ or ]), it seems type checking is inevitable.

回答1:

Type checking is not the only option to do what you want, but definitely one of the easiest:

import numpy as np  def to_str(var):     if type(var) is list:         return str(var)[1:-1] # list     if type(var) is np.ndarray:         try:             return str(list(var[0]))[1:-1] # numpy 1D array         except TypeError:             return str(list(var))[1:-1] # numpy sequence     return str(var) # everything else 

EDIT: Another easy way, which does not use type checking (thanks to jtaylor for giving me that idea), is to convert everything into the same type (np.array) and then convert it to a string:

import numpy as np  def to_str(var):     return str(list(np.reshape(np.asarray(var), (1, np.size(var)))[0]))[1:-1] 

Example use (both methods give same results):

>>> to_str(1.) #float '1.0' >>> to_str([1., 1., 1.]) #list '1.0, 1.0, 1.0' >>> to_str(np.ones((1,3))) #np.array '1.0, 1.0, 1.0' 

回答2:

If you don't know what is the type of var you can check type using

from collections import Iterable if isinstance(var,Iteratable):     mystring=''.join(map(str,var)) else:     mystring=str(var) 

回答3:

Maybe what you're looking for is repr()

It's the opposite of the eval function.

Here's what eval does:

eval('[1,3]') # [1, 3] 

Here's what repr does:

repr('example') # "'example'" repr(0.1) # '0.1' repr([1,2]) # '[1,2]' 

回答4:

str is able to convert any type into string. It can be numpy.array / list / float

# using numpy array new_array = numpy.array([1,2,3]) str(new_array) >> '[1 2 3]'  # using list new_list = [1, 2, 3] str(new_list) >> '[1, 2, 3]'  # using float new_float = 1.1 str(new_float) >> '1.1' 

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