Invalid syntax error using format with a string in Python 3 and Matplotlib

Question

The code: ``` #/usr/bin/env python3 # -*- coding: utf-8 -*- import numpy as np import matplotlib.pyplot as plt from sympy.solvers import * from sympy import * from matplotlib import rcParams rcParams['text.latex.unicode'] = True rcParams['text.usetex'] = True rcParams['text.latex.preamble'] = '\usepackage{amsthm}', '\usepackage{amsmath}', '\usepackage{amssymb}', '\usepackage{amsfonts}', '\usepackage[T1]{fontenc}', '\usepackage[utf8]{inputenc}' f = lambda x: x ** 2 + 1 #f = lambda x: np.sin(x) / x x = Symbol('x') solucion = solve(x**2+1, x) fig, ax = plt.subplots() x = np.linspace(-6.0, 6.0, 1000) ax.axis([x[0] - 0.5, x[-1] + 0.5, x[0] - 0.5, x[-1] + 0.5]) ax.spines['left'].set_position('center') ax.spines['right'].set_color('none') ax.spines['bottom'].set_position('center') ax.spines['top'] ax.spines['left'] ax.spines['bottom'] ax.xaxis.set_ticks_position('bottom') ax.yaxis.set_ticks_position('left') ax.grid('on') ticks = [] for i in range(int(x[0]), int(x[-1] + 1), 1): ticks.append(i…

Accepted Answer

The `u'...'` syntax for string literal was removed in Python 3.0

- All strings are unicode strings in Python 3.

From docs:

String literals no longer support a leading `u` or `U`.

So, you can simply drop the `u'...'` in Python 3:

```
r'$Solución \; {}\; :\; {}\$'.format(i, value)
```

Note: The `u'...'` syntax has been re-introduced in Python 3.3(thanks to @Bakuriu for pointing that out).

And the new re-introduced string-prefix syntax looks like this:

```
stringprefix    ::=  "r" | "u" | "R" | "U"
```

Python 2 string-prefix syntax:

```
stringprefix    ::=  "r" | "u" | "ur" | "R" | "U" | "UR" | "Ur" | "uR"
                     | "b" | "B" | "br" | "Br" | "bR" | "BR"
```

Invalid syntax error using format with a string in Python 3 and Matplotlib

Solution

Problem