[pypy-issue] Issue #3026: struct format does not support space in struct.py (pypy/pypy)

[Aure at bitbucket.org]

New issue 3026: struct format does not support space in struct.py
https://bitbucket.org/pypy/pypy/issues/3026/struct-format-does-not-support-space-in

Aurélien Lambert:

While trying to import pytz in brython \(which is using pypy pure python implementation of libraries\), I encountered a bug on `struct.py` \([https://bitbucket.org/pypy/pypy/src/18626459a9b2/lib\_pypy/\_struct.py](https://bitbucket.org/pypy/pypy/src/18626459a9b2/lib_pypy/_struct.py)\): spaces are not allowed in the format string. This behavior is inconsistent with python documentation \(“Whitespace characters between formats are ignored;”\) and does not happen with the compiled struct module.

```python
from test.struct import calcsize # local copy of pypy struct.py
calcsize('>4s c 15x 6l') # format from pytz

>>> StructError:   is not a valid format
```

This is due to the functions `getmode` and `getNum` not checking for whitespaces. This implementation of `getNum` gets rid of middle spaces.

```python
def getNum(fmt,i):
    num=None
    cur = fmt[i]
    while cur == ' ':
        i += 1
        cur = fmt[i]
    while ('0'<= cur ) and ( cur <= '9'):
        if num == None:
            num = int(cur)
        else:
            num = 10*num + int(cur)
        i += 1
        cur = fmt[i]
    return num,i
```

Getting rid of end spaces will be little trickier because all the function use `getNum` like this:

```python
    while i<len(fmt):
        num,i = getNum(fmt,i)
        cur = fmt[i]
        [...]
        i += 1
```

I suggest either to systematically use `fmt = fmt.rstrip()`, either to change the behavior of `getNum`

```python
def getNum(fmt,i):
    num=None
    cur = fmt[i]
    while cur == ' ':
        i += 1
        cur = fmt[i]
    while ('0'<= cur ) and ( cur <= '9'):
        if num == None:
            num = int(cur)
        else:
            num = 10*num + int(cur)
        i += 1
        cur = fmt[i]
    i += 1
    while i < len(fmt) and fmt[i] == ' ':
        i += 1
    return num,i,cur
```

And use it like this

```python
    while i<len(fmt):
        num,i,cur = getNum(fmt,i)
        [...]
```